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OVERVIEW . .. . . . . . . . . . . .. . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . .. . . . 1 INTRODUCTION . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 What is Shareware . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . 1 LICENSE, WARRANTY AND REGISTRATION . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 LICENSE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 WARRANTY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . 2 REGISTRATION . . . . . . . . .. . . . . . . .. . . .. . . .. . . . . . . .. . . .. . . .. . . . . . 2 IS REGISTRATION WORTHWHILE? . . . . . . . . . . . . . . . . . . . .. . . .. . . .. . .. 2 Serial Port Fundamentals . .. . . . . . . .. .. .. . . . . . . . . . .. . . . .. . . .. .. . . . 3 The 8250 UART family . .. . .. .. .. .. . . .. . . .. .. .. .. .. . . . . .. .. . .. . . 3 Purpose of the port . . . .. . . . . . .. . .. .. . . . .. .. . . . . . . .. . . . . . .. . 3 INTERNAL PORT DETAILS . . .. . . . .. . . .. .. . . . . .. .. . . . . .. . . .. . .. .. . . 3 The Interrupt Connection . . .. . .. . . . .. . . . .. . . . .. . . . .. . . . .. .. . 4 THE PORT REGISTERS LiteComm Communications ToolBox Copyright 1987 - 1991 Information Technology, Ltd. Information Technology 5 Park Blvd. Lincoln, RI 02865 (401) 724-2730 OVERVIEW INTRODUCTION TM The LiteComm ToolBox is a set of powerful routines designed to provide easy access to the full capabilities of the PC's asynch- ronous communications ports. The LiteComm ToolBox provides interrupt-driven, buffered communications support on COM1 through COM4 simultaneously. Now you can quickly incorporate sophis- ticated communications support in your applications without hav- ing in-depth knowledge of how the hardware functions. LiteComm is the result of meeting a need for communications in CAD/CAM applications created for a client company. Each version of the LiteComm ToolBox depends upon its respective host compil- er. The 'Lite' in LiteComm refers to the high granularity of the product. LiteComm, in simple applications, adds about 5K bytes of overhead. Yet it provides a highly reliable base on which to build. As you use LiteComm, you will find yourself in good company. Li- teComm is currently in use at ATT, IBM, NASA, and the Associated Press, to name a few of our users. In addition, LiteComm has been featured in at least one book, Straight Talk by Charles Bowen and Stewart Schneider. Finally, the Turbo Pascal version of LiteComm is the basis for the Async Professional package from Turbopower Software. What is Shareware Shareware is a "try before you buy" means of software distribu- tion. If you find a shareware product useful, pay the registra- tion fee, and let the authors know that you support their efforts. Information Technology is a member of the Association of Share- ware Professionals (ASP). ASP wants to make sure that the shareware principle works for you. If you are unable to resolve a shareware-related problem with an ASP member by contacting the member directly, ASP may be able to help. The ASP Ombudsman can help you resolve a dispute or problem with an ASP member, but does not provide technical support for members' products. Please write to the ASP Ombudsman at P.O. Box 5786, Bellevue, WA 98006 or send a Compuserve message via easyplex to ASP Ombudsman 70007,3536. 1 LICENSE, WARRANTY AND REGISTRATION LICENSE Information regarding the LiteComm license will be found in the file LICENSE.DOC, on the distribution diskette. Please read this information. By your use of LiteComm, we assume that you agree to the terms and conditions of the license agreement. If you are interested in a site license for LiteComm, please see the file SITELICE.DOC on the distribution disk. WARRANTY The LiteComm warranty is in the distributed file WARRANTY.DOC. Be sure you read the warranty before using LiteComm. REGISTRATION Registration information and an order form are in the file REGISTER.DOC. IS REGISTRATION WORTHWHILE? LiteComm is a package undergoing continuing development. We are constantly reviewing the product to make it smaller, faster, more reliable, and easier to use. Since its introduction in mid 1987, we have made significant changes to the LiteComm kernel, the heart of the ToolBox, to improve efficiency and reliability. We have also delivered to registered users protocol engines, LXM - the Xmodem engine, which supports Xmodem and Xmodem-1K; and LWXM - the Windowed Xmodem engine. We also provide a version of the Compuserve QUICKB protocol, specially adapted for use with the LiteComm ToolBox. We are also reviewing other protocol engine implementations. In this release of LiteComm, for example, we have added support for True YModem and ZModem. The small model library, as enhanced will always be offered as a shareware product. 2 Serial Port Fundamentals The 8250 UART family This portion of the manual provides you with some details about the working of the 8250 (and related) UART'S, the basic component of your system's serial port. Some close compatibles use en- hanced versions of this chip, such as the 16450 and 16550. LiteComm works successfully with such devices. If you have questions about the type of serial port you are using, refer to the manufacturer's documentation. If your serial port does not use an 8250 or similar chip, LiteComm will not function. Purpose of the port The serial port converts information from the form in which it is used within your system, to a form that can be easily used out- side your system. Modern computers, by design, are parallel in nature. By this we mean that information travels through the computer's circuitry as whole units or as multiples of whole units. In the IBM PC and related systems, information travels as bytes (8 bits at a time), as words (16 bits at a time), or, on 80386 and 80486 based systems, as double words (32 bits at a time). Within the computer, such arrangements are convenient and fast. When the computer must transfer information to an external de- vice, data path width is a problem. To provide a parallel path between the computer and external devices, there would have to be enough data lines or circuits between the two to satisfy the data path. For most modern computer systems, this would mean a mini- mum of 8 data lines, not counting any additional control information that also might be necessary. For certain newer systems, the requirement might be for as many as 32 data lines. In effect, it might be necessary to have several different ver- sions of a device, dependent upon the data path width of the computer. The purpose of a serial port is to convert the information from its internal, parallel form, to a more common, external form and back. By using such an approach, we simplify the interconnection of devices, reducing information to its lowest common denomina- tor, the bit. It allows us to transfer information 1 bit at a time, using a single data path, between devices. The real beauty of this approach is that, by agreeing on how this external form appears, each device can hide the details of how it works, and still do the required task. INTERNAL PORT DETAILS In this section we discuss the fundamental working of serial ports on the IBM PC and close compatible systems. It is not es- sential that you understand this material thoroughly to be successful with LiteComm. Still, it may help to answer some more 3 important questions that may arise as you proceed with your de- velopment. The Interrupt Connection The PC is an interrupt driven system. This is a sophisticated way of saying that the PC can pay attention to several internal de- vices. It doesn't have to check on, or poll, them periodically. The method by which 80x86 family interrupts work is elegant in its simplicity. When a device needs the attention of the system, its asserts a control signal and identifies itself with a number ranging from 0 to 255. On the basic PC, the numbers used range from 8 through 15 decimal. PC components translate the identification to a memory location by multiplying the identifi- cation by 4. The system then simulates a special form of a call to the routine whose address is at that memory location. Since it is impossible to predict when a device will require attention, the system uses the far address of the routine, both segment and offset, therefore the 4. Once called, this routine, called the Interrupt Service Routine or ISR, has a duty to save the state of the system when the in- terrupt occurred. It must take care of the interrupt as quickly as possible, and return control to the interrupted process. It also must be aware that, while it is doing its work, other, more important devices may require attention, too. One device that requires constant attention is the system clock that ticks roughly 18 times per second. In part, the PC makes provision for this by prioritizing the interrupt scheme. The ISR must allow for this by reenabling the interrupt control system as rapidly as it is practical to do so. The PC's interrupt struc- ture, if left undisturbed, will prevent interrupts of the same or lower priority from occurring. To help you organize your thoughts, the standard identifications for the first two serial ports on the system are 12 (0C) and 11 (0B) for ports 1 and 2 respectively. However, the intrreupt structure of the PC is far from perfect. Systems that use the original ISA buss have a shortcoming. Only one device is allowed to occupy an interrupt vector or location at a time. This is in contrast to systems that employ either the micro-channel buss or the EISA buss. In these latter two buss designs, multiple devices may occupy a single intterupt location. As you can see, dealing with the PC's interrupt structure is not for the faint of heart. It requires a significant amount of knowledge, and close attention to detail. LiteComm takes care of these details for you. You are free to focus on your applica- tion, treating the serial port in much the same way that you would any DOS file. 4 THE PORT REGISTERS The 8250 port is fully programmable. LiteComm has already taken care of the intricacies of this programming. But some additional information about each register used in the serial port may be of use when you are attempting to communicate with an external de- vice. For the sake of this discussion, we use the basic register numbers. The actual register number used is the register number referenced below used as an offset to a base port number. For COM1 (port 1), this base is 3F8(hexadecimal). register 0 - transmit/receive register 0 - transmit/receive register 0 - transmit/receive In normal operation, the ISR reads individual characters from register 0 when the become available. The ISR writes to register 0 when the transmitter portion of the 8250 is ready to accept a character. register 0 - baud rate selection register 0 - baud rate selection register 0 - baud rate selection During initialization, register 0 is part of the mechanism that sets baud rate. During this process, register 0 and its compan- ion register 1 specify the baud rate divisor (not the actual baud rate). The baud rate divisor is a value that, when divided into a given, preset constant, yields the desired baud rate. To set the baud rate, you must first enable access to this mode. This is done by writing a value of 80H to register 3, the line control register. Once complete, the least significant byte (LSB) of the divisor is written to register 0; the most significant byte is written to register 1. Access to the normal modes of registers 0 and 1 are reenabled by writing any value less than 80H to the line control register. Of course, only certain values less than 80H would be meaningful (see the line control register descrip- tion below). register 1 - interrupt enable register 1 - interrupt enable register 1 - interrupt enable Values written to register 1 control the conditions that will cause the 8250 to interrupt the system. There are four possible conditions that can cause interrupts: 1. A character has been received (RDI) (RDI) (RDI) 2. The transmitter is ready to send a character (TDI) (TDI) (TDI) 3. An error or BREAK signal has been detected (ERI) (ERI) (ERI) 4. A modem status signal has changed (MSI) (MSI) (MSI) The designations, in parentheses, are for our purposes only. They are not 'standard' designations. To enable a particular type of interrupt, you must set the corresponding bit in a byte to a 1, then write the byte to register 1. To reset (ignore) the condi- tion, set the corresponding bit to 0. The diagram that follows shows the bit positions the correspond to the various conditions described above. 5 N/A N/A N/A N/A Modem Error/ Xmit Recv Status Break Ready Char 7 6 5 4 3 2 1 0 Register 1 Bit Definitions register 1 - baud rate selection register 1 - baud rate selection register 1 - baud rate selection See the description under register 0, baud rate selection. register 2 - interrupt identification register 2 - interrupt identification register 2 - interrupt identification Register 2, in normal operation, acts as a companion to register 1. Register 1 determines the conditions that can cause an interrupt. Register 2 identifies the specific condition that caused the interrupt, when more than one condition is enabled. The least significant 3 bits of the register contain the identi- fication. See the diagram of register 2 that follows. N/A N/A N/A N/A N/A Int ID Int ID Int Pend 7 6 5 4 3 2 1 0 Register 2 Bit Definitions Since it is possible, even likely, that more than one condition may occur simultaneously, bit 0 tells whether all conditions that currently exist have been handled. When bit 0 has a value of 0 (yes zero), there are conditions waiting to be handled. When bit 0 has a value of 1, all outstanding conditions have been handled. Bits 2 and 1 taken together identify the actual cause of the in- terrupt. Again, because of the multiple conditions that may occur, the 8250 presents the conditions in a prioritized order. When bits 2 and 1 have a value of 3 (the most important), an ERI ERI ERI condition exists. The actual error can be read from the line status regis- ter(register 5). Reading this register also clears the condition. When a value of 2 is present, an RDI RDI RDI condition has occurred, and a character should be read from port 0. If the character is not read quickly enough, a data overrun error may occur, indicating the loss of a character. When bits 2 and 1 have a value of 1, a TDI TDI TDI condition has occurred and a character may be written to register 0. A value of zero in bits 2 and 1(least important) shows that one or more of the modem status lines (so called) have changed. The condition can be cleared by reading the contents of the modem status register, register 6. 6 register 3 - line control register 3 - line control register 3 - line control The line control register gives the means for setting those val- ues that affect the way in which the serial port appears to the outside world. It is through this register that the program es- tablishes character length, parity, and other significant values. Indirectly, register 3 also plays a role in setting the speed (baud rate) of the port. (See the description of registers 0 and 1.) Baud Send Force Parity Enable Stop Char Char Div Break Parity Type Parity Bits Len Len 7 6 5 4 3 2 1 0 Register 3 Bit Definitions register 4 - modem control register 4 - modem control register 4 - modem control The modem control register permits control of the two modem- re- lated signals that the serial port generates as an output. The signals are Request To Send, RTS RTS RTS and Data Terminal Ready, DTR DTR DTR. These two signals are handshaking signals, since they, in part, help a connected device figure out the state of the connection. These signals were originally designated to be used in a specific fashion. Yet, manufacturers of specific devices have used them to meet their needs. Your success or failure in dealing with any specific device may depend, in part, on your understanding of how the device's manufacturer uses these signals. LiteComm provides you the means for manipulating these signals in a variety of ways. You will notice in the register 4 diagram, below that some addi- tional positions are identified. N/A N/A N/A Enable OUT2 OUT1 RTS DTR Loop (reqd) 7 6 5 4 3 2 1 0 Register 4 Bit Definitions LiteComm controls these additional positions for your benefit. Only one deserves mention, the position labeled OUT2 OUT2 OUT2. It is necessary for this position to have a value of 1 for the serial port to function as an interrupting device. Since LiteComm relies on interrupts to perform it's job, it always sets this position correctly. register 5 - line status register 5 - line status register 5 - line status The program normally reads the line status register when an ERI ERI ERI condition occurs. Each bit of the character returned has sig- nificance, as shown in the accompanying diagram. Using the ap- propriate functions in LiteComm, you can interrogate the value in this register, and test for the various conditions using the 7 LiteComm- provided definitions. Note that, due to the special nature of the BREAK BREAK BREAK signal, LiteComm treats this one condition as a separate entity. Time Shift Hold Recd Frame Parity Over Data Out Reg Reg Break Error Error Run Rec'd Empty Empty Error 7 6 5 4 3 2 1 0 Register 5 Bit Definitions register 6 - modem status register 6 - modem status register 6 - modem status Just as the serial port can generate certain handshaking signals, it also can read, and report on the status of similar signals that an external device generates. In their original form, these signals had special significance for connections between a terminal and a modem. We refer you to our comments, above, about present day use of the handshaking signals. One special note is appropriate here. The modem status register provides two types of information. The most significant 4 bits (see the diagram) show the current state of the 4 covered sig- nals. The least significant 4 bits show which, if any, of the signals have changed state (from zero to one, or vice-versa), since the last time the register was interrogated. LiteComm up- dates its internal tables with this value in real-time, and re- ports the results when asked to do so. You can test the signals individually or in combination using the LiteComm- provided definitions. DCD RI DSR CTS Delta Delta Delta Delta Carr Ring Data Clear DCD RI DSR CTS Det Ind Set Rd Send 7 6 5 4 3 2 1 0 Register 6 Bit Definitions The LiteComm Connection In the design of LiteComm, we have purposely 'hidden' many underlying details we presented above. Often, you will have little use for this additional information. This is particularly true of most of the applications with which you will come into contact. In most applications, you probably will open the port or ports, set the necessary parameters and modem control signals, and do nothing more than read and write characters using one or more of the LiteComm functions. The beauty of LiteComm's design is that its high degree of granularity doesn't force you to pay the price of dragging along functions that you are not using. The information that we presented above will help you when it is necessary to communicate with a device that requires special handshaking considerations, such as a cash drawer. You also may need the information we presented if you intend to use serial ports beyond COM2 (serial port 2). 8 Finally, by presenting the information that we have supplied, we hope to gain a more informed user. Communications programming is not the black art that some would have you believe, although it can easily seem that way at times. Of the calls we receive with questions, more than 75 per cent could be answered by the caller himself with a more thorough understanding of the underlying concepts and rules. ToolBox NOTES AND WARNINGS Note: Note: Note:Special warning for old-style PC owners There is a known problem with serial ports on older systems. Due to a problem with old-style 8250 and 16450 UARTS, it is possible for the transmitter to stop functioning. This problem is cuased by a loss of interrupts under load. While software workarounds exist, we have decided not to include such workarounds in Lite- Comm. Inclusion of this logic would result in added overhead to all LiteComm users. If you believe you are experiencing this problem, please contact us. Note: Note: Note:Open Required Before you can send or receive information on a serial port using the ToolBox, you must use the open function to enable the line. This function initializes the UART with the correct parameters, and introduces the UART into the interrupt structure of the PC. The ToolBox will detect, and report, any errors that you may make in selecting the port or specifying the initial parameters. Note: Note: Note:Close Required The ToolBox interfaces directly with the interrupt structure of the PC. It is critical before exiting a program that has opened a serial port that the serial port is closed with the close func- tion. Since it is possible for a program to terminate abnormally, the open function installs an exit routine that will automatically close any open ports. Good programming practice demands that your program should close the ports explicitly. By so doing, you may avoid problems in the future if we find it necessary to remove the auto-close functionality. Further, the auto-close functionality drops all modem handshaking signals ab- solutely, while an explicit close can decide whether to drop these signals. If you are unaware of exit functions, check your compiler's documentation for the atexit() function for a complete explanation. Review the description of the comm_close() function, as well. Failure of the open function can result from several causes, im- proper parameters to the open function, a non-existant serial port or insufficient memory. The memory is needed for the re- quested buffers and related control structures for the port. Memory for the transmit and receive buffers as well as the port control block is allocated from free memory. It is your responsibility to insure that adequate memory is available for 9 this purpose. This requires no particular action on your part. If you use LiteComm in combination with other packages, the other packages may place specific restrictions on your use of free memory. Note: Note: Note:Handshaking Signals The ToolBox will, at your option, assert both the DTR and RTS signals when you open the port. If you do not select this option you must use the lc_setmdm function to assert (raise) this sig- nal. In addition, some modems and other devices may require you to assert either the DTR (Data Terminal Ready) or the RTS (Re- quest To Send) signal before they will respond to data. Please note that the use of handshaking signals is HIGHLY hardware- dependant. The ToolBox provides all the functionality necessary for you to implement almost any handshaking scheme that might be required. WARNING WARNING WARNING Due to the use of all available interrupt modes of the 8250, one user has discovered an unusual set of circumstances that can be troublesome. If the 8250 chip detects an error condition, such as a parity error, framing error, or data overrun error, it causes an interrupt to which the ToolBox will respond. If these errors occur frequently enough, the ToolBox code will spend too much time handling the errors, and lose characters, causing additional errors. If you encounter a situation in which your application appears to behave erratically, especially at higher speeds, investigate the following table. Possible Error Conditions Is the cabling to the other device sound and solidly con- nected? Are any of the signals in the cable 'floating' or are they all properly terminated? Is the other device functioning properly? We have encountered situations in which a serial port on some devices tends to be sloppy in terms of voltage levels, bit timings, and similar problems. Any, or all, these situations can cause the erratic operation to which we referred. WARNING WARNING WARNING Unless you are very familiar with the interrupt structure of the PC, do not attempt to manipulate the interrupt enable flag out- side the ToolBox. The ToolBox sets and clears the interrupt en- able flag at appropriate times and assumes that it has sole control over the flag. Note: Note: Note:Byte Alignment Unless otherwise specified, all library functions use byte structure alignment. This alignment results from the way in which the interrupt handler was developed in assembly language. 10 NEW IN VERSION 6.00 In version 6.0, we have again improved on the assembly language interrupt handlers. In addition, there have been significant changes in the supporting functions to tighten the code. The result is smaller applications, often able to operate at higher baud rates. Other additions to LiteComm in version 6.0 include fully automatic flow control using either software or hardware. Both variants are programmer-configurable. This should simplify things for some users. In version 6.0, LiteComm will attempt to insure that you are at- tempting to open a valid COM port. If LiteComm believes that the port is not valid, it will return an error from comm_opn. The addition of a global error variable should help in determining the source of the error. See the section on LiteComm functions for additional information. And we have addressed an area that we have always considered a LiteComm weakness. In previous versions of LiteComm, it was pos- sible to detect an receive error globally, yet not know when it occurred. With version 6.0, LiteComm now buffers errors in the same way that it buffers incoming characters. At your option, you can retrieve the error status associated with a character. There have been numerous, less significant additions to LiteComm, as well. Many are the result of user-feedback. Nearly all are aimed at making your job simpler. BEYOND COM2 THE ToolBox METHODOLOGY In the design of the original PC, and in subsequent variations such as the PC/AT, there was only provision for two serial ports. Many manufacturers of add-in products, both serial ports and in- ternal modems have added the capability to support 1 or more additional ports beyond the COM2 limit. Generally, this can cause problems in the PC since there is no room in the interrupt re- quest scheme for additional levels of interrupts. There are no designated interrupt vector for other additional ports. The ToolBox approach to resolving these issues is to permit the programmer a degree of control over the parameters that govern the interrupt mechanism for COM3 and COM4. Specifically, these parameters are: 1. The interrupt request (IRQ) bit that is used to mask the 8259 interrupt controller. 2. The interrupt vector number (not address) to which the port is attached. 11 3. The base i/o register for the port itself. Of course, it we assume that the port is an 8250 UART or compatible device. Again, the LiteComm ToolBox will not function with non-8250 type devices. Before you attempt to use COM3 and/or COM4, you must figure out from the port's documentation, the appropriate values for these three parameters. As distributed, the ToolBox assumes the following: Port COM 3 COM 4 IRQ Bit 4 3 Vector 0CH 0BH Base Register 3E8H 2E8H You may change any of these values by using the _portchg function described below, but only before you open the port with comm_opn. Once the port has been opened, _portchg is ineffective. _portchg will not work on COM1 or COM2. At present, LiteComm is not compatible with multiport boards such as the Digiboard. The structure of these boards generally re- quires additional programming to be used effectively. If you want to use such a board with LiteComm, please contact us directly for information on custom modifications to LiteComm. We have performed such modifications for other LiteComm users. CAUTIONS There is an intimate relationship between the IRQ setting and its related interrupt vector. In the PC, this relationship is con- trolled, in part, by the 8259 interrupt controller that is set during BIOS initialization. In brief, the BIOS settings for the PC (and most close compa- tibles) establish IRQ0 as vector number 08h, and subsequent IRQ levels at increasing vector numbers. These vector numbers (or types in INTEL terms) act as a cpu- directed call table to loca- tions in the lowest 1K of system memory. We can alter how the system responds to a given interrupt by replacing or changing the values in the associated vector position to point to a routine that we supply. Judging from the questions asked by some users of LiteComm, there is evidently some misunderstanding about using ports beyond COM2, and how this all relates to your hardware. Before you can suc- cessfully use COM3 or COM4, you must consider the following: Does the hardware permit a change to the base port and/or the interrupt vector to which the port responds? Some expansion cards will support changing one and not the other, causing po- tential hardware conflicts and lost data. 12 Does the hardware permit reassignment of the IRQ priority? Some expansion cards permit you to alter the IRQ priority, some won't. Briefly, from the previous discussion, any change to the IRQ priority must allow a corresponding change to the interrupt vector number. Without this capability, reprogram- ming of the 8259 chip would be required. Many add-on cards permit this dual change simply by making a single switch or jumper setting. Unfortunately, the documenta- tion for these cards generally assumes that you are aware of the dual nature of the IRQ vector relationship, and may leave you with the impression that you are changing one and not the other. In most circumstances, this is not so. The point to all this is that LiteComm can only provide as much support as the hardware permits, or is capable of responding to. If you wish to use other than the default base port, interrupt vector, or irq priority for COM3 or COM4, then your expansion card must be able to support the new values; in other words, these values are all hardware-provided, and are recognized by the LiteComm software. If your hardware does not permit changing a value, LiteComm cannot improve the situation. We should, at this point, add one final caution about how inter- rupt priorities function, and their relationship to the irq bit that you may select. The standard PC permits 8 interrupt priority levels. The PC-AT and later systems permit a total of 16 inter- rupt priority levels. Regardless of system type, the programmable timer has the highest priority; the parallel printer port has the lowest priority. When an interrupt occurs, the interrupt controller (8259 chip) masks out all other interrupts from the priority of the interrupting device and all lower priority de- vices. As an aid to making COM3 and COM4 fit, LiteComm supports inter- rupt chaining for the COM3 and COM4 ports, on PS/2 and other mi- crochannel systems. If you use COM3 or COM4, when an interrupt occurs, the kernel will attempt to determine if the interrupt was caused by the supported port or from another source. Only the PS/2 and similar systems can reliably support interrupt chaining; it is NOT a restriction that we impose. The restriction lies in the design of the original PC and PC-AT buss structure. If the kernel determines that the supported port did not cause the interrupt, an automatic chain to the original interrupt han- dler for that interrupt level (IRQ level) will take place. This allows you to "patch in" or share the available interrupt vec- tors. If you intend to use other than the library-provided defaults, be sure that you understand the interrupt mechanism. The use of the automatic chaining described above can be particularly trouble- some under some circumstances, resulting in loss of interrupts and, potentially, a system crash. 13 Note: Note: Note:DO NOT DO NOT DO NOT attempt to mix the ToolBox functions with other seemingly- related functions (such as the serial port BIOS calls provided in both Turbo and Microsoft C). At least two users have attempted to use only the receive portions of LiteComm, while resorting to the BIOS functions to send characters or adjust port parameters such as baud rate. The results, at best, have been failure of the user's application to function, and, at worst, total system lockup. This mix of functions is NOT supported and must not be used. If you attempt such a mix, we cannot help you. If you chose to share the interrupt vectors for COM1 or COM2, you must be certain to open COM1 (COM2) last. The interrupt chaining mechanism only works with COM3 and COM4. Failure to follow this caution will result in a total loss of function of COM3 (COM4). In addition, the ports should be opened in descending order of the planned baud rate, i.e. the faster port should be opened first, the slower port should be opened last. Whenever possible or practical, you will obtain best results by using the same baud rate on both ports. One final caution is in order. One or two users have attempted to trace through the interrupts as they occur using software based debuggers. This is a risky proposition at best since most debuggers work by tapping into, and disturbing, the interrupt mechanism. If you feel you must use a debugger, try to avoid the kernel routines of LiteComm, or use a hardware-based debugger such as Periscope. 14 INSTALLATION PACKAGE CONTENTS Your distribution diskette contains many files that are important to you. See the file PACKING.LST on the distribution disk for a list of the files that you should have received. INSTALLING LITECOMM LiteComm is installed with the INSTALL utility that we provide on the distribution diskette. To use this utility, follow the easy steps below: 1. Make a copy of the distribution diskette before beginning. 2. Insert the distribution diskette in your diskette drive. 3. Make the distribution diskette the default drive by typing ei- ther A:<ENTER> or B:<ENTER>. 4. Type the command INSTALL<ENTER>. INSTALL will present you with a screen that specifies the in- stallation default values. You may freely edit them before pro- ceeding with the installation. Use the arrow keys to move between the various options. When you are satisfied with your responses, press the <PAGE-DOWN> key to proceed with installation. INSTALL will create several directories on the target disk drive. These directories do not have to exist before you start INSTALL. After copying the necessary files, INSTALL will decompress the files into their final form and clean up after itself. By default, install will create the following directories: LITECOMM Header Files LITECOMM\LIB PreBuilt Libraries LITECOMM\SOURCE Package Source Code If you prefer, of course, you may install LiteComm manually by copying all of the distributed EXE files to your destination disk. Then execute each to decompress it, with the exception of INSTALL. Finally, delete each of the EXE files to clean up your disk. They will no longer be needed. REBUILDING THE LIBRARIES We have provided you with the source code for LiteComm so that you may modify our product to meet special needs. We encourage you to use the provided MAKE files to accomplish this. They were used in constructing the libraries you have just installed and will make the task decidedly simpler. the make files for Turbo C are TURBOCOMM.MAK and TLCP.MAK. The make files for Microsoft C are MSCCOMM.MAK and MLCP.MAK. 15 We have had a report from one user that the make files are not compatible with the version of the make utility provided with the IBM C compiler, even though IBM's product is derived from Micro- soft C. Unfortunately, we do not support the IBM product as we have no way of assuring compatibility. We do understand, however, that the Microsoft libraries are fully compatible. GENERAL NOTES LiteComm and its related libraries make extensive use of parame- ters defined in the included header files. Your programs should always use the same header file parameters. While every effort will be made in future releases of LiteComm to preserve the val- ues as currently provided, we cannot guarantee that changes will never occur. The surest way to safeguard your efforts is to use the defined parameters. Then, when new versions of LiteComm are released, you need only recompile and relink to insure consistency. In the discussion of the various functions that follows, you should assume that any references to the port variable refer to a variable or constant that may take on a value of from 1 to 4. No other values are acceptable, and will be rejected. While we feel that LiteComm is written in the most efficient way possible, commensurate with good programming practice, we cannot be responsible for variations caused by hardware configurations or other factors beyond our control. LiteComm has been tested on the IBM PC-AT, IBM PS/2 and several compatible systems such as the Zenith and Wyse equivalents. LiteComm has not been tested in environments in which other software, most significantly TSR (terminate and stay resident) modules exist. Some TSR programs that "steal" interrupts for their purposes present an unfavorable environment to other programs that rely on the interrupt struc- ture of the computer. If you experience erratic behavior with LiteComm in a TSR-type situation, try executing your application without the TSR module being present. If the problems you have experienced disappear, suspect the TSR module. Conversely, LiteComm provides an excellent vehicle for supporting TSR programs that you may write. Since the package is fully reentrant, your only concern need be with those aspects of TSR programs are of normal concern, e.g., the non reentrant nature of DOS. LiteComm only uses DOS functions when opening and closing ports. It may therefore be safely used in a TSR environment. As an example, we have included the program SPM as part of this re- lease. SPM is a background Serial Port Monitor that is available as a separate shareware product. SPM was developed using Lite- Comm. USE WITH MULTITASKING ENVIRONMENTS Some users have made attempts at using LiteComm with multitasking environments such as Quarterdesk's DesqView. Use of LiteComm in 16 such an environment is certain to be affected by the way in which the multitasking behaves with respect to interrupts. We recog- nize that DesqView has achieved a great deal of popularity among so-called power users. Still, LiteComm was not explicitly de- signed for such environments, and its performance may suffer as a result. NOTES ON RING DETECTION Several users have reported problems in consistently detecting a ringing telephone by checking the state of the RI (Ring Indica- tor) signal. The problem seems highly dependent on the type of modem that is being used, since this signal comes from the modem. If the duration of the signal is too short, the program may miss the signal as the modem toggles it. One workaround that has been successfully is to check the RICHG bit returned from lc_mstat, rather than the RI bit. The RICHG bit will be set when the RI bit comes one and again when the RI bit goes off. This is the method employed in the check_for_call function. 17 FUNCTION REFERENCE GENERAL INFORMATION In the following pages, we provide the detailed information about each available LiteComm ToolBox function. Each function defini- tion includes, at a minimum, a summary of how to code the func- tion, a description of what the function does, and an indication of those values, if any, that the function might return. Where appropriate, we include additional documentation about the function. Some definitions include examples, in the sense of code fragments illustrating the function's usage. More impor- tantly, some definitions include additional notes and warnings as well as references to other functions within the package. We have made every effort to insure that the documentation of the functions is complete and accurate. The style and manner of the documentation assume that the reader is thoroughly familiar with the elements of C syntax and common conventions. FLOW CONTROL In version 6 of LiteComm, we have incorporated fully automatic flow control, using either software, sometimes called XON-XOFF control, or hardware using the handshaking signals. Note: Note: Note:It is not valid to have both methods of flow control active at the same time. Failure to observe this restriction can cause unpredictable results. GLOBAL ERROR VARIABLE Version 6 of LiteComm has a global error variable that is set by each of the LiteComm functions. The variable, _lc_error _lc_error _lc_error, is de- fined in LITECOMM.H. Possible values are in the file LITE- COMM.ERR. Examining the contents of _lc_error can help you diagnose and correct problems. 18 _portchg SUMMARY #include <litecomm.h> int _portchg(port, base, irq, vector) unsigned port; unsigned base; unsigned vector; char irq; DESCRIPTION Changes one or more of the critical parameters for COM3 or COM4. This function must be used before the opening port to be effec- tive. To leave any of the parameters at its default value, make the corresponding entry 0. Note that vector is a vector number, not an address or pointer. The irq parameter is NOT the irq (interrupt request) number, but the irq mask. The following lines, reproduced from 'litecomm.h' help illustrate this idea. #define IRQ1 0x10 /* int req mask for port 1 - irq4 */ #define IRQ2 0x08 /* int req mask for port 2 - irq3 */ Note: Note: Note:The value for irq4 is NOT 4, but a character in which bit 4, using INTEL's bit numbering, has a value of 1. Thus, to use irq priority 1 as the irq for either COM3 or COM4, you would specify 0x02 as the value of irq when calling _portchg. The default parameters are in the litecomm.h include file. If you intend to change the default irq settings, you also MUST MUST MUST make a corresponding change to the vector number. See the accom- panying documentation about using COM3 and COM4 for additional details. Failure to follow this rule may make the port appear to be nonfunctional. The _portchg function does NOT check to determine that you have provided both an IRQ mask AND a new vector number. Example Example Example if (_portchg(port, 0x408, 0, 0, 0) == -1) { printf("Error Changing Port %d\n", port); exit(1); } RETURN VALUES Returns 0 if the function is successful, -1 if you attempt to change a port other that 3 or 4. 19 comm_opn SUMMARY #include <litecomm.h> int comm_opn(port, baud, parity, datab, stopb, inbufsz, outbufsz, raisemdm) unsigned port; unsigned baud; unsigned parity; unsigned datab; unsigned stopb; unsigned inbufsz; unsigned outbufsz; DESCRIPTION Opens the specified port for use and attaches an interrupt han- dler to DOS for the port. Optionally, comm_opn will raise the DTR and RTS modem control signals, if the value of raisemdm is TRUE. The function allocates, from the heap, space for the CCB (com- munications control block), space for the interrupt handler's stack, and buffers for input and output of the specified sizes. The minimum value for inbufsz is 128; the minimum size for out- bufsz is 64. If sufficient memory is available and the parameters are correct, the port will be set to the parameters (baud rate, word length, stop bits) used when the function is called. The memory overhead associated with opening a port can be approximated by adding about 1.2K bytes to the buffer sizes specified. comm_opn installs an exit handler using the atexit() function to protect DOS from problems that might arise if a program using LiteComm fails. Still, it is sound practice to close a port opened in this manner using comm_close explicitly in your program to gain maximum control over the port. The baud parameter is an unsigned integer that specifies the baud rate you intend to use, e.g., 4800. The other parameters passed to the function should be from the parameter set in the lite- comm.h include file. Example Example Example Below are two examples of using comm_opn, the first letting comm_opn raise the modem control signals, the second using two function calls to do the same thing. The result of each example is the same, an open port on which the DTR and RTS signals have been raised. Example 1 Example 1 Example 1 if (comm_opn(port, 1200, NPARITY, BIT8, STOP1, 256, 256, TRUE) == - 1) { printf("Error Opening Port %d\n", port); exit(1); 20 } Example 2 Example 2 Example 2 if (comm_opn(port, 1200, NPARITY, BIT8, STOP1, 256, 256, FALSE) == - 1) { printf("Error Opening Port %d\n", port); exit(1); } lc_setmdm(port, (DTR | RTS)); RETURN VALUES Upon successful open, the function returns port. If any error occurs, despite the type, the function returns -1. 21 comm_close SUMMARY #include <litecomm.h> int comm_close(port, dropmdm) unsigned port; DESCRIPTION This function is the companion to comm_opn and, in effect, per- forms the opposite action. Comm_close detaches the library rou- tines from the interrupt handler, and reconnects the previous interrupt handler. Comm_close also releases all allocated memory used for the buff- ering and control structures described under comm_opn. If the value of dropmdm is non-zero, the port is closed absolutely, and all modem control signals are dropped. If the value of dropmdm is zero, the port is closed conditionally, and both the DTR and RTS signals will be left in their current state. Since comm_opn installs an exit handler using the atexit function in both Turbo C and Microsoft C, you are not required to close explicitly an open port. However, if you do not explictly close the port, you will lose control over the handling of the DTR and RTS signals since the built-in exit handler uses the absolute form of the close. Example Example Example These are two equivalent examples of the comm_close function. The first uses the absolute port close, the second uses two function calls to do the same thing. Example 1 Example 1 Example 1 comm_close(port, TRUE); /* absolute close */ Example 2 Example 2 Example 2 lc_clrmdm(port, (RTS | DTR)); /* lower modem control */ comm_close(port, FALSE); /* conditional close */ RETURN VALUES If any error occurs, despite the type, the function returns -1. 22 comm_setup SUMMARY #include <litecomm.h> int comm_setup(port,baud,parity,datab,stopb) unsigned port; unsigned baud; unsigned parity; unsigned datab; unsigned stopb; DESCRIPTION The comm_setup function is a subset of the comm_opn function and the remarks made in the description of comm_opn regarding the port parameters apply. This function is useful if you wish to change the basic commu- nication parameters of the specified port that has already been opened without comm_close'ing the port. Example Example Example if (comm_setup(port, 1200, NPARITY, BIT8, STOP1) == -1) { printf("Error Changing Port %d\n", port); exit(1); } RETURN VALUES If any error occurs, despite the type, the function returns -1. SEE ALSO comm_opn 23 lc_vport SUMMARY #include <litecomm.h> COMM *lc_vport(port) DESCRIPTION lc_vport is a macro that validates that the port number specified is correct and has been opened with the comm_opn function. It may be of use to you in writing certain applications. RETURN VALUES If the port is valid and has been opened, returns a pointer to the CCB (communications control block) for the port. Returns NULL if an error occurs; 24 lc_icnt, lc_ocnt SUMMARY #include <litecomm.h> int lc_icnt(port) int lc_ocnt(port) unsigned port; DESCRIPTION These functions may be used to determine the number of characters currently in the input(lc_icnt) or output(lc_ocnt) buffers for the port. Example Example Example #include <litecomm.h> if (lc_icnt(port)) /* anything received ? */ puts("Characters waiting in input"); RETURN VALUES Both functions return -1 if an error occurs (port not open or invalid port number). The lc_icnt() function returns the number of characters in the input buffer; lc_ocnt() returns the number of characters remaining in the transmit buffer. 25 lc_mstat SUMMARY #include <litecomm.h> int lc_mstat(port) unsigned port; DESCRIPTION May be used to determine the last known state of the modem- supplied handshake signals. These may be tested using the values in the include file litecomm.h. The handshake signals consist of a byte in which the bits 4-7 contain the current state of the signals (such as Clear To Send or CTS). Bits 0-3 contain information regarding whether individual signals have changed. lc_mstat always returns the current values of the signals in bits 4-7. Bits 0-3 will reflect which, if any, of the signals has changed. The easiest approach to dealing with the returned value is to test bits 0-3 (the DELTA or change bits) for a non-zero value. If any non-zero value is found in bits 0-3, one or more signals have changed _____ ___ ____ ____ __ ________ since the last call to lc_mstat. Note: Note: Note:The functions resets the DELTA bits. The value obtained from bits 4- 7 will correctly reflect the current state of the signals. To examine individual signals, litecomm.h has #defined symbols for the change bits ,e.g., CTSCHG, and for the signals themselves ,e.g.. CTS. Example Example Example int curstat; curstat = lc_mstat(port); /* get curent values */ if (curstat & DCDCHG) /* DCD changed ? */ if (! (curstat & DCD)) /* carrier still on */ puts("Remote is off-line, carrier lost"); RETURN VALUES If the port is valid and open, returns the current modem status bits. Returns -1 if an error occurs. SEE ALSO lc_got??? 26 lc_got??? SUMMARY #include "litecomm.h" unsigned port; lc_gotcts(port); lc_gotdsr(port); lc_gotri(port); lc_gotdcd(port); lc_gotctschg(port); lc_gotdsrchg(port); lc_gotrichg(port); lc_gotdcdchg(port); DESCRIPTION This set of 8 macros makes the job of testing the individual mo- dem status signals simpler. The macros rely upon the lc_mstat function and you should refer to the description of that function for additional information. SEE ALSO lc_mstat 27 lc_estat SUMMARY #include <litecomm.h> int lc_estat(port) unsigned port; DESCRIPTION May be used to determine the last known state of the serial port's error status bits. These may be tested using the values in the include file litecomm.h. The errors that are detected and reported include: ORUNERR - failure to fetch a character from the port before the next character arrived. Usually a problem in the interrupt han- dler. PARERR - One or more characters were received in which the parity of the character(s) did not match the current parity setting of the port. Can be caused by line noise, or by other causes. FRMERR - A framing error has occurred. A character arrived that had too few or (more likely) too many bits. Usually caused by line noise. RETURN VALUES If the port is valid and open, returns the current error status bits. Returns -1 if an error occurs. 28 lc_getw SUMMARY #include <litecomm.h> int lc_getw(port) unsigned port; DESCRIPTION Reads a character from the serial port's input buffer. Waits in- definitely until a character is available. If the port is dis- connected for any reason, this function will cause a system hang if called, so its use should be carefully controlled. RETURN VALUES Returns the next available character in the input buffer for the port. Returns -1 if the port is not active, or if an invalid port number is specified. 29 lc_setmdm SUMMARY #include <litecomm.h> int lc_setmdm(port, newset) unsigned port; unsigned newset; DESCRIPTION Set one or more of the modem control signals. Because of the need to have OUT2 set for interrupt support, the function always pro- vides the correct setting for this bit. Use the symbolic #defines found in the litecomm.h file. Many applications will not require this function, if they allow comm_opn to raise these two signals. More sophisticated applications may be required to control either or both of the signals to provide handshaking with an external device. Example Example Example /* raise the RTS modem control signal */ lc_setmdm(port, RTS); /* raise both RTS and DTR */ lc_setmdm(port, (RTS | DTR)); RETURN VALUES Returns 0 if the operation was successful, returns -1 otherwise. SEE ALSO comm_opn, lc_clrmdm, lc_togmdm, lc_setdtr, lc_setrts 30 lc_setdtr, lc_setrts SUMMARY #include "litecomm.h" unsigned port; lc_setdtr(port); lc_setrts(port); DESCRIPTION lc_setdtr and lc_setrts are macros designed to help make your code more explicit. Both macros use the lc_setmdm function to set the DTR and RTS signals. Note that no effort is made to preserve the current modem signal status. That is use of the lc_setdtr macro will cause RTS to drop. The converse is true of lc_setrts. SEE ALSO lc_setmdm 31 lc_clrmdm SUMMARY #include <litecomm.h> int lc_clrmdm(port, newset) unsigned port; unsigned newset; DESCRIPTION Companion to the setmdm function. Clears the modem control sig- nals RTS or DTR or both. Because of the need to have OUT2 set for interrupt support, the function always provides the correct set- ting for this bit. Use the symbolic #defines found in the lite- comm.h file. Generally, this function only has value if you trying to implement some form of hardware handshaking with another device. The comm_close function will lower both RTS and DTS automatically, if told to do so. Example Example Example /* lower the RTS modem control signal */ lc_clrmdm(port, RTS); /* lower both RTS and DTR */ lc_clrmdm(port, (RTS | DTR)); RETURN VALUES Returns 0 if the operation was successful, returns -1 otherwise. SEE ALSO comm_close, lc_setmdm, lc_togmdm 32 lc_togmdm SUMMARY #include <litecomm.h> int lc_togmdm(port, newset) unsigned port; unsigned newset; DESCRIPTION Companion to setmdm function. Inverts (flip-flops) the modem control signals RTS or DTR or both. Because of the need to have OUT2 set for interrupt support, the function always provides the correct setting for this bit. Use the symbolic #defines found in the litecomm.h file. This function may have value if you are trying to implement hardware handshaking. Example Example Example /* ** change the RTS modem control signal to its other ** state (e.g. if raised, lower, and if lowered, raise */ lc_togmdm(port, RTS); RETURN VALUES Returns 0 if the operation was successful, returns -1 otherwise. SEE ALSO lc_setmdm, lc_clrmdm 33 lc_xoff SUMMARY #include <litecomm.h> int lc_xoff(port, flag) unsigned port; int flag; DESCRIPTION If flag is non-zero, the function enables automatic software flow control function. If flag is zero (the default setting), automatic flow control is disabled. When enabled, the LiteComm kernel will automatically transmit the OFF character when the input buffer is approximately 2/3 full and will automatically recognize an OFF character sent by the other device. If the other device transmits an OFF character, the ker- nel will refuse to send any characters until the condition is cleared by receipt of the ON character or by disabling software flow control altogether. The recognition functionality is implimented in the kernel. As a result, the transmit buffer will continue to accept input from your program until the buffer fills completely, even though the information will not be sent. Once the matching ON character is received, the contents of the transmit buffer will be sent rapidly to the other device. It is possible that the rate with which characters are sent when this occurs may cause problems for the other device, depending on its ability to handle the data flow. If you intended to implement a protocol that might include the ON or OFF characters, be sure to disable the automatic flow control. Failure to do so may result in a system hang. By default, software flow control uses the XON-XOFF flow control characters. You may change the characters to suit your applica- tion by using the lc_setxon and lc_setxoff functions. RETURN VALUES Returns 0 if the operation was successful, returns -1 otherwise. SEE ALSO lc_gotxoff, lc_putxoff, lc_setxon, lc_setxoff 34 lc_gotxoff SUMMARY #include <litecomm.h> int lc_gotxoff(port) unsigned port; DESCRIPTION If the OFF character has been received, this function will return a non-zero value. A zero is returned if the OFF character is never received, or if the ON character is detected. Note: Note: Note:Unlike older versions of LiteComm, lc_gotxoff is now useful only for information. It does not alter the way in which software flow control operates. RETURN VALUES Returns a nonzero value if the OFF character was detected, zero if an OFF character was not detected, or if the ON character is detected. Will return -1 in the case of an error. SEE ALSO lc_xoff, lc_putxoff, lc_setxon, lc_setxoff 35 lc_putxoff SUMMARY #include <litecomm.h> int lc_putxoff(port) unsigned port; DESCRIPTION See below for the values returned. If the LiteComm kernel has sent the OFF character. Note: Note: Note:Unlike older versions of LiteComm, this function provides information only. Use of the function has no effect upon software flow control. RETURN VALUES Returns a nonzero value if an OFF character was sent to the other device, zero if an OFF was not sent, or if the ON character has been sent. Will return -1 in the case of an error. SEE ALSO lc_xoff, lc_putxoff, lc_setxon, lc_setxoff 36 lc_setxon, lc_setxoff SUMMARY #include "litecomm.h" int lc_setxon(port, xonchar); int lc_setxoff(port, xoffchar); unsigned port; unsigned char xonchar; unsigned char xoff char; DESCRIPTION These functions are part of the software flow control functonal- ity of LiteComm. By default, LiteComm's software flow control uses the XON-XOFF character scheme. If your application has dif- ferent requirements, use the lc_setxon function to change the ON character, lc_setxoff to set the OFF character. RETURN VALUES Both functions return a -1 if an error occurs. Both return a value of zero (0) if there is no error. SEE ALSO lc_xoff, lc_gotxoff, lc_putxoff 37 lc_sethwflow SUMMARY #include "litecomm.h" int lc_sethwflow(port, flowtype) unsigned port; unsigned char flowtype; DESCRIPTION This function specifies the type of hardware flow control to use and activates hardware flow control. The point at which hardware flow control is activated is the same as for software flow con- trol. You have complete control over which hardware signals are used for flow control. For output (from the port) control specify ei- ther USEDSR or USECTS. For input (to the port) control, specify either USEDTR or USERTS. Since most hardware flow control schemes employ both input and output flow control, you should OR the re- quired values together, as shown in the example. Hardware flow control remains in effect until you issue the lc_clearhwflow function. Note: Note: Note:The flow control scheme assumes that the input flow control signal (RTS or DTR) have been set to the correct starting value by the program. Thereafter, LiteComm flow control will manage the signals. Example Example Example /* Use RTS-CTS flow control */ if lc_sethwflow(port, (USECTS | USERTS)) puts("Error setting flow control"); RETURN VALUES The function returns a value of zero (0) if successful. If an error occurs, the function returns -1. SEE ALSO lc_xoff, lc_clearhwflow, lc_puthwstop, lc_gothwstop 38 lc_clearhwflow SUMMARY #include "litecomm.h" int lc_clearhwflow(port) unsigned port; DESCRIPTION Immediately deactivates hardware flow control. Any untransmitted characters will be sent as rapidly as possible. RETURN VALUES If successful, returns a value of zero (0). Retuirns -1 if an error occurs. SEE ALSO lc_sethwflow, lc_puthwstop, lc_gothwstop 39 lc_puthwstop SUMMARY #include "litecomm.h" int lc_puthwstop(port) unsigned port; DESCRIPTION Indicates whether or not LiteComm has instructed the remote de- vice to stop transmitting. RETURN VALUES If an error occurs, returns a value of -1. If input flow control has not been asserted, returns a value of zero (0). If input flow control has been asserted, returns a positive, non-zero value; SEE ALSO lc_sethwflow, lc_gothwflow 40 lc_gothwstop SUMMARY #include "litecomm.h" int lc_gothwstop(port) unsigned port; DESCRIPTION Indicates whether or not LiteComm has been instructed by the re- mote device to stop transmitting. RETURN VALUES If an error occurs, returns a value of -1. If output flow control has not been asserted, returns a value of zero (0). If output flow control has been asserted by the remote device, returns a positive, non-zero value; SEE ALSO lc_sethwflow, lc_puthwflow 41 lc_get SUMMARY #include <litecomm.h> int lc_get(port) unsigned port; DESCRIPTION Read a character from the serial port's input buffer. Discard (ignore) the matching status value Example Example Example if ((ch = lc_get(port)) != -1) /* any chars? */ ch &= 0x7f; /* mask parity */ RETURN VALUES Returns the next available character in the input buffer for the port. If you specified other than NO PARITY when you opened the port, you may have to mask (make zero) the parity bit before you use the character. Returns -1 if the port is not active, or if there are not characters in the port's buffer. SEE ALSO lc_getstat, wait, purge 42 lc_getstat SUMMARY #include "litecomm.h" int lc_getstat(port, ch, status); unsigned port; unsigned char *ch; unsigned char *status; DESCRIPTION This function retrieves the next character and its corresponding error status from the LiteComm buffers, if there are characters available. The status that is returned is the value of the error status register at the time the character was received. For more information about the error status see the lc_estat function. Note: Note: Note:The variables for ch and status must both be pointers. RETURN VALUES If there are characters available and no other errors occur, the function will return a value of zero (0). If there are no other characters, or if some other error occurs, the function returns a value of -1. SEE ALSO lc_get, lc_estat, wait, purge 43 wait SUMMARY #include "litecomm.h" int wait(port, secs, sig_to_check); unsigned port; int secs; unsigned char sig_to_check; DESCRIPTION The wait function waits for secs seconds for input from the des- ignated port before returning. Optionally, wait will also monitor one or more of the modem status signals and return if the signal drops. Secs must be greater than zero. If you do not want wait to moni- tor a modem status signal, specify zero (0) as sig_to_check. To specify a signal, use the constants, such as DCD, found in lite- comm.h. Note: Note: Note:Valid signal values are CTS, DCD, DSR, and RI. RETURN VALUES If a character is retrieved within the time allowed, the function returns the character. If a character is not available in the specified time, if the specified signal is lost, or if some other error occurs, the function returns a value of -1. SEE ALSO lc_get, lc_getstat 44 purge SUMMARY #include "litecomm.h"; void purge(port); unsigned port; DESCRIPTION The purge function discards any characters received until there are no more incoming characters for a period of 1 second. RETURN VALUES This function does not return any value; SEE ALSO wait 45 lc_peek SUMMARY #include <litecomm.h> int lc_peek(port) unsigned port; DESCRIPTION Look at the next character in the serial port's input buffer. Do not remove the character from the buffer. RETURN VALUES Returns the next available character in the input buffer for the port, but does not remove the character from the buffer. This allows the application to look-ahead by one character in a nondestructive fashion. See additional comments under lc_get re- garding parity. Returns -1 if the port is not active, or if there are no characters in the port's buffer. 46 lc_put SUMMARY #include <litecomm.h> int lc_put(port,ch) unsigned port; char ch; DESCRIPTION Place a character into the serial port's output buffer. RETURN VALUES Returns 0 if successful. Note that this does not guarantee that the character has been sent, only that no errors were detected, and that there was room in the transmit buffer for the character. Characters are sent from the transmit buffer when the system has time to send them, assuming all conditions for transmission are satisified. Returns -1 if the port is not active, or if there no room in the port's buffer. 47 lc_gets SUMMARY #include <litecomm.h> int lc_gets(port, buff, cnt) unsigned port; char *buff; int cnt; DESCRIPTION Read a stream of, at most, cnt characters from the serial port's input buffer into the buff location. Ignore and discard any sta- tus information. This function is not sensitive to the NULL character. See lc_get for additional information. Example Example Example char * j; int k; int wrk; j = buff; /* point to top of our buffer */ k = sizeof(buff); /* set chars needed to fill */ do { wrk = lc_gets(port, j, k); if (wrk != -1) /* got something ? */ { j += wrk; /* bump buffer pointer */ k -= wrk; /* decrement chars req'd */ } } until (k <= 0); RETURN VALUES Returns the count of characters transferred into buffer, or -1 if an error occurs. 48 lc_puts SUMMARY #include <litecomm.h> int lc_puts(port, buff, cnt) unsigned port; char *buff; int cnt; DESCRIPTION Place a stream of, at most, cnt characters into the serial port's output buffer. Any required parity will be supplied by the serial port itself. Example Example Example char * j int j; int sent; j = buff; k = sizeof(buff) do { sent = lc_puts(port, j, k); if (sent > 0) { j += sent; k -= sent; } } until (k <= 0); RETURN VALUES Returns the number of characters placed into the buffer. Note that this does not guarantee that the characters have been sent. The number of characters transferred into the output buffer may be less than the actual request. Returns 0 if any error occurs, or if there is no room in the port's buffer. 49 lc_flush SUMMARY #include <litecomm.h> int lc_tflush(port) int lc_rflush(port) int lc_flshtrue(port, ch) int lc_nflush(port, cnt) unsigned port; char ch; int cnt; DESCRIPTION The lc_?flush functions remove characters from the specified buffer and discard them; untransmitted characters in the transmit buffer are NEVER sent; unprocessed characters in the receive buffer are lost. Do not try to use the lc_tflush to force char- acters to be transmitted. The tflush function unconditionally empties the transmit buffer, discarding any unsent characters. lc_tflush empties the port's transmit buffer immediately. lc_rflush empties the port's receive and status buffers im- mediately. lc_flshtrue will continually dispose of received characters until the function finds the character ch. Use caution with this one since it does not detect port number errors, and may appear to seize the system. lc_nflush flushes, at most, cnt characters from the port's re- ceive and status buffers. RETURN VALUES lc_flshtrue returns no values. lc_tflush and lc_rflush return 0 if successful and -1 if an error occurs. lc_nflush returns the number of characters flushed from the receive buffer or 0 when there are no characters to flush, or when an error occurs. 50 lc_sbrk SUMMARY #include <litecomm.h> int lc_sbrk(port) lc_gotbrk(port) unsigned port; DESCRIPTION lc_sbrk() generates a BREAK signal using a particular character- istic of the 8250 UART family to generate an accurate BREAK at any baud rate. BREAKs generated in this manner are timed based upon the baud rate at which the 8250 is currently initialized. This function may or may not work correctly with other than the actual 8250 UART or its relatives. RETURN VALUES lc_gotbrk returns a nonzero value if a break signal has been re- ceived on the specified port. It returns zero otherwise. lc_sbrk Returns 0 if successful. Returns -1 if the port is not active. 51 newtimer_s SUMMARY include "lctime.h"; void newtimer_s(et, sec); EVENT *et; unsigned sec; int check_timer(et); EVENT ev; DESCRIPTION The newtimer_s function creates an 'event timer' that will expire in sec seconds. This function relies upon the calculation of an absolute time value and does not tie into any system interrupt, permitting as many independent timeout timers as required by your application. The check_timer function examines the contents of an event timer created by newtimer_s with respect to the current date and time, and indicates whether the timer has expired. Do not attempt to use check_timer against a variable that was not set by newtimer_s. If you do so, the results are unpredictable and may result in a seeming system hang. 52 Example Example Example EVENT cdtimer; newtimer_s(&cdtimer, 30); /* 30 second timer */ while( ! check_timer(cdtimer)) if (check_for_call(port) > 0) { cprintf("Incoming call\r\n"); return(1); } cprintf("No calls in 30 seconds\r\n"); return(0); RETURN VALUES The newtimer_s function returns no value but initializes a structure that represents a point in time sec seconds from the time that newtimer_s was called. The check_timer function returns a nonzero value if the specified event timer has expired, a value of zero otherwise. 53 BBS SUPPORT FUNCTIONS INTRODUCTION In this chapter, we discuss a set of utility functions that were originally developed as a part of a BBS package with one of our registered users. Not only are they useful, in and of them- selves, but they also act as examples of using the LiteComm ToolBox in situations that puzzle some users. ADDITIONAL NOTES The use of any of the functions that follow in this section re- quire that you define, in your code, three modem setup strings with the names MODEMSET0, MODEMSET1, and MODEMSET2, and must be pointers to characters. In addition, they must be defined as global variables, and must be public (i.e., not static). Below, we show one way to do this. Example Example Example char istrng0[] = "ATZ\r"; char istrng1] = "ATT E0 V0 X1 M1\r"; char istrng2[] = "ATS0=1\r"; char *MODEMSET0; char *MODEMSET1; char *MODEMSET2; void main(void) { ... MODEMSET0 = &istrng0[0]; MODEMSET1 = &istrng1[0]; MODEMSET2 = &istrng2[0]; ... } Experienced C programmers will readily recognize that this is not necessarily the best approach. But it does serve to illustrate clearly the ideas involved. Be sure to define MODEMSET0, 1, and 2 as pointers to characters as shown above, and NOT as arrays. It is a fine destinction in C, but an important one. 54 check_for_call SUMMARY include "lcbbs.h"; int check_for_call(port) unsigned port; DESCRIPTION This function checks the status of the specified port to deter- mine whether (1) there is an incoming call and (2) waits for up to 30 seconds for carrier to be established with the caller if the phone rang. Please note that this function relies upon, in part, the HAYES command set. Use with other than HAYES- compat- ible modems may result in unexpected hangs or other, unpredict- able results. The function assumes that the modem parameters have been set in the manner described in the reset_modem func- tion. In the event that a wrong number call is received, check_for_call will automatically disconnect by lowering the DTR(Data Terminal Ready) signal momentarily, then automatically call the reset_mo- dem function. See the notes at the beginning of this chapter, and in the discussion of the reset_modem function. This method of disconnecting, while absolute, will only work correctly if you HAVE NOT set your modem to ignore the DTR signals, as is possible with some modems. Please consult your modem's documentation for additional detail. RETURN VALUES If the phone was not ringing, the function returns a value of zero. If detects a ring was detected, but does not detect carrier within 30 seconds, the function will return a value of -1 after forcing a disconnect and resetting the modem. Otherwise, the function returns the numeric result code, in integer form. It is the programmer's responsibility to interpret and act upon the result code. For the function to work properly, the modem must be set to return numeric result codes rather than word re- sult codes. 55 get_modem_reply SUMMARY include "lcbbs.h" int get_modem_reply(port) unsigned port; DESCRIPTION The get_modem_reply function is intended for use after a command has been issued to a HAYES compatible modem. To operate proper- ly, the modem must be set to return numeric responses rather than word responses. The function returns to the caller when one of the following occurs: No response from the modem within 1 second. More than 2 response characters received before a <CR> is de- tected. A <CR> is received from the modem. Due to the internal logic employed, the programmer should call this function, or purge the receive buffer, after each command sent to the modem. Failure to do so will result in improper in- terpretation of the result codes returned. RETURN VALUES Returns a value of -1 if there is no response from the modem within 1 second. Otherwise returns the integer result code. If the modem has not been set to return numeric result codes, the results are unpredictable. 56 reset_modem SUMMARY include "lcbbs.h" int reset_modem(port) unsigned port; DESCRIPTION The reset_modem function initializes the modem to a known state, suitable for use with the other bbs functions, and based upon a set of initialization strings provided by the user's program. See the notes at the beginning of this chapter for additional information regarding the way that this must be done. Because the modem-related functions in this section make certain assumptions about the modem, your initialization strings should include, at a minimum, the following: No command echo Detect carrier Return numeric result codes Answer the phone on the first ring (if you need to use the check_for_call function) A sample set of initialization strings is shown at the start of this chapter. If you require any additional information on these or related options, please consult your modem's documentation. RETURN VALUES The reset_modem function returns the same result code as those specified for get_modem_reply. 57 disconnect SUMMARY include "lcbbs.h" void disconnect(port) unsigned port; DESCRIPTION The disconnect forcibly disconnects the modem from the telephone line by lowering the DTR signal momentarily. You must be certain that your modem IS NOT set to ignore the DTR signal for the function to work properly. RETURN VALUES Disconnect returns no values. 58 HAYES MODEM FUNCTIONS Note: Note: Note:When using the following functions, you must include the file litehcm.h in your program. litehcm.h automatically includes the litecomm.h header file. FUNCTIONS lch_codeset lch_dial lch_fduplex lch_hduplex lch_greg lch_sreg lch_offcarr lch_oncarr lch_offecho lch_onecho lch_hook lch_redo lch_numres lch_wrdres lch_codesoff lch_codeson lch_pulse lch_tone lch_speaker _retset _rettype SUMMARY #include <litehcm.h> int lch_codeset(port,mode) int lch_dial(port,dstr) int lch_fduplex(port) int lch_hduplex(port) int lch_greg(port,reg) int lch_sreg(port,reg,value) int lch_offcarr(port) int lch_oncarr(port) int lch_offecho(port) int lch_onecho(port) int lch_hook(port,hmode) int lch_redo(port) int lch_numres(port) int lch_wrdres(port) int lch_codesoff(port) int lch_codeson(port) 59 int lch_pulse(port) int lch_tone(port) int lch_speaker(port,spkmode) int _retset() int _rettype() unsigned port; unsigned mode; char *dstr; unsigned reg; int value; unsigned hmode; unsigned spkmode; DESCRIPTION The values to be used with mode, hmode, and spkmode are defined symbolically in the #include file, litehcm.h. The lch_codeset lch_codeset lch_codeset function allows you to change the set of codes returned by the modem when an action is specified. lch_dial lch_dial lch_dial instructs the modem to dial the number contained in dstr. Do not include the dialing (ATD) prefix, or the trailing <\r>. These are provided by the function. You may include non- numeric characters that are acceptable to your modem, since the function does not check the contents of dstr. The dialing is in the last known dialing mode, either pulse or tone. If you use the lch_pulse or lch_tone functions, then dialing will be done in the mode that was last correctly enabled. If you have not exercised these functions, then dialing occurs in the modems default or power-up mode. The lch_hduplex lch_hduplex lch_hduplex and lch_fduplex lch_fduplex lch_fduplex functions place the modem into local echo and remote echo modes respectively. The lch_greg lch_greg lch_greg function requests that the modem report the current value of S-register reg. Reg must be in the range 0 to 13. Use the lc_gets, or similar function, to retrieve the modem's re- sponse. Specifying a register outside the 0 to 13 range will cause a return of -1. lch_sreg lch_sreg lch_sreg is the companion to lch_greg, with the same restric- tions. Sets the S-register reg to the value contained in value. If value contains -1, then the register is reset to its default (power-up) value. The function checks the value to be certain that it is within the limits specified for the particular regis- ter, and returns a value of -1 if the value is outside the predefined limits. lch_offcarr lch_offcarr lch_offcarr enables modem carrier detect, but disables the mo- dem's carrier signal. The lch_oncarr companion enables both car- rier detect and the modem's carrier signal. When lch_offcarr is used the modem will receive data but will be unable to send data. 60 The lch_offecho lch_offecho lch_offecho and lch_onecho lch_onecho lch_onecho functions determine whether com- mands sent to the modem are echoed back to the sending program. With echo turned off, the modem will continue to accept commands, but will not try to redisplay the command's characters. lch_hook lch_hook lch_hook allows you to control the status of the modem's tele- phone line connection. See your modem's documentation and the include file for additional information. The lch_redo lch_redo lch_redo function instructs the modem to repeat the last command sequence executed. Generally, this function is of great- est value in redialing numbers that are busy, although its use is not restricted to that. The way in which your modem responds to commands is determined, in part, by the lch_wrdres lch_wrdres lch_wrdres and lch_numres lch_numres lch_numres functions. If you call lch_wrdres, then modem responses use the English language re- sponse codes, e.g,. CONNECT or OK. Calling lch_numres instructs the modem to respond with code numbers only from the currently selected response set, see the lch_codeset function. You may use the functions lch_codeson lch_codeson lch_codeson and lch_codesoff lch_codesoff lch_codesoff to specify whether you want your modem to send back response codes when it receives a command string. In a sense, these act as companions to the lch_xxxecho functions above. Use the lch_speaker lch_speaker lch_speaker function to control the modem's internal speaker, if it has one. See litehcm.h for the applicable codes. The _retset _retset _retset and _rettype _rettype _rettype functions return, respectively, the last known command set (lch_codeset) and last known result type (lch_wrdres, lch_numres). These functions (_retset, _rettype) are only of value when used with the companion functions. GENERAL REMARKS Several considerations are in order if you intend to use the Hayes ToolBox functions. You are responsible for checking the return codes from the modem once you have given modem a command. To make the task easier, we suggest that you turn OFF command echo. Then you won't have to worry about separating commands from responses. Finally turn ON numeric responses to make the interpretation of result codes easier and faster. Note: Note: Note:Be sure that you allow adequate time between commands for the modem to process the command and respond. Failure to observe this rule may result in commands being misinterpreted or "lost." You can monitor the number of characters in the receive buffer to help you with the timing. Or alternatively, check the response after each command. The latter approach is more in line with what we believe to be good programming practice. 61 RETURN VALUES All functions return a value of -1 if a port or other error oc- curs, zero otherwise. 62 INDEX INDEX INDEX _lc_error, 18 get_modem_reply, 56, 57 _portchg, 12, 19 handshaking, 7, 8, 9, 10, 18, _retset, 59, 61 30, 32, 33 _rettype, 59, 61 HAYES, 55, 56, 59, 61 HAYES MODEM FUNCTIONS, 59 16450, 3, 9 16550, 3 identification, 4, 6 8250, 3, 5, 6, 9, 10, 12, 51 INSTALL, 15 8259, 11, 12, 13 INSTALLATION, 15 interrupt, 4, 5, 6, 9, 10, Alignment, 10 11, 12, 13, 14, 16, 19, 20, ASP, 1 22, 28, 30, 32, 33, 52 baud, 5, 6, 7, 11, 14, 20, 23, 51 IRQ, 11, 12, 13, 19 BBS SUPPORT FUNCTIONS, 54 ISA, 4 ISR, 4, 5 BIOS, 12, 14 lc_clearhwflow, 38, 39 BREAK, 5, 8, 51 buffer, 20, 25, 29, 34, 42, lc_clrmdm, 30, 32, 33 46, 47, 48, 49, 50, 56, 61 lc_estat, 28, 43 buss, 4, 13 lc_flush, 50 lc_get, 42, 43, 44, 46, 48 C, 14, 15, 16, 18, 22, 54 chain, 13 lc_gets, 48, 60 check_for_call, 17, 55, 57 lc_getstat, 42, 43, 44 COM1, 1, 5, 12, 14 lc_getw, 29 COM2, 8, 11, 12, 14 lc_got, 26, 27 lc_gothwstop, 38, 39, 41 COM3, 11, 12, 13, 14, 19 COM4, 1, 11, 12, 13, 14, 19 lc_gotxoff, 34, 35, 37 comm_close, 20, 22, 32 lc_icnt, 25 comm_opn, 11, 12, 20, 22, 23, lc_mstat, 17, 26, 27 24, 30 lc_ocnt, 25 comm_setup, 23 lc_peek, 46 control, 3, 4, 5, 7, 8, 9, lc_put, 47 10, 11, 16, 18, 20, 22, 24, lc_puthwstop, 38, 39, 40 30, 32, 33, 34, 35, 36, 37, lc_puts, 49 38, 39, 40, 41, 61 debuggers, 14 lc_putxoff, 34, 35, 36, 37 Digiboard, 12 lc_sbrk, 51 lc_setdtr, 30, 31 disconnect, 55, 58 lc_sethwflow, 38, 39, 40, 41 divisor, 5 DTR, 7, 10, 20, 21, 22, 30, lc_setmdm, 10, 30, 31, 32, 33 31, 32, 33, 38, 55, 58 lc_setrts, 30, 31 echo, 57, 60, 61 lc_setxoff, 34, 35, 36, 37 lc_setxon, 34, 35, 36, 37 EISA, 4 ERROR, 5, 6, 10, 11, 18, 21, lc_togmdm, 30, 32, 33 22, 23, 24, 25, 26, 28, 35, lc_vport, 24 36, 37, 38, 39, 40, 41, 43, lc_xoff, 34, 35, 36, 37, 38 44, 48, 49, 50, 62 lch_codeset, 59, 60, 61 event, 52, 53, 55 lch_codesoff, 59, 61 flow control, 11, 18, 34, 35, 36, 37, 38, 39, 40, 41 lch_codeson, 59, 61 INDEX INDEX INDEX lch_dial, 59, 60 status, 5, 6, 7, 8, 11, 26, lch_fduplex, 59, 60 27, 28, 31, 42, 43, 44, 48, lch_greg, 59, 60 50, 55, 61 lch_hduplex, 59, 60 TSR, 16 UART, 3, 9, 12, 51 lch_hook, 59, 61 USECTS, 38 lch_numres, 59, 61 lch_offcarr, 59, 60 USEDSR, 38 lch_offecho, 59, 61 USEDTR, 38 USERTS, 38 lch_onecho, 59, 61 vector, 4, 11, 12, 13, 19 lch_redo, 59, 61 lch_speaker, 59, 61 wait, 42, 43, 44, 45 lch_sreg, 59, 60 warning, 9, 10 warranty, 2 lch_wrdres, 59, 61 workarounds, 9 length, 7, 20 libraries, 15, 16 Xmodem, 2 license, 2 Xmodem-1K, 2 XON-XOFF, 18, 34, 37 memory, 4, 9, 10, 12, 20, 22 YModem, 2 micro-channel, 4 multitasking, 16, 17 ZModem, 2 newtimer_s, 52, 53 NULL, 24, 48 open, 8, 9, 10, 11, 12, 14, 20, 21, 22, 25, 26, 28 OUT2, 7, 30, 32, 33 parity, 7, 10, 20, 23, 28, 42, 46, 49 PC, 3, 4, 9, 10, 11, 12, 13 port, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 16, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 55, 56, 57, 58, 60, 62 priority, 4, 13, 19 PS/2, 13, 16 purge, 42, 43, 45, 56 register, 5, 6, 7, 8, 12, 43, 60 Registration, 1, 2 reset_modem, 55, 57 RI, , 17, 44 RTS, 7, 10, 20, 22, 30, 31, 32, 33, 38 Shareware, 1, 2, 16