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Personal Communications Library For the C Language (PCL4C) USERS MANUAL Version 3.3 Aug 3, 1992 This software is provided as-is. There are no warranties, expressed or implied. Copyright (C) 1992 All rights reserved MarshallSoft Computing, Inc. Post Office Box 4543 Huntsville AL 35815 Voice 205-881-4630 FAX 205-881-4630 BBS 205-880-9748 PCL4C Users Manual Page 1 C O N T E N T S Chapter Page 1.0 Introduction................................................3 1.1 User Support............................................4 1.2 A Typical Application...................................5 1.3 Installation............................................6 2.0 Library Organization........................................7 2.1 Initialization & Termination............................7 2.2 Configuration...........................................7 2.3 Modem Control & Status..................................8 2.4 Serial I/O..............................................8 2.5 Error Detection.........................................9 2.6 General Support.........................................9 3.0 Library Overview...........................................10 3.1 Memory Models..........................................10 3.2 Compilers Supported....................................11 3.3 Using the Library......................................12 3.4 Example Programs.......................................12 3.5 Compiling & Linking....................................13 4.0 Talking to Your Modem......................................14 4.1 Modem Standards........................................14 4.2 Flow Control...........................................15 4.3 Modem Initialization...................................16 5.0 Problems...................................................17 6.0 Serial Communications......................................18 6.1 Communications Basics..................................18 6.2 Standard Port Addresses................................19 6.3 RS232 Signals..........................................20 6.4 National INS8250, INS16450, and INS16550 UARTs.........21 6.5 Register Summary.......................................22 7.0 Terminal Emulator Program (TERM)...........................24 8.0 Legal Issues...............................................25 8.1 Registration...........................................25 8.2 License................................................26 8.3 Warranty...............................................26 9.0 Summary....................................................27 9.1 Revision History.......................................27 9.2 Function Summary.......................................28 9.3 Further Reading........................................28 10.0 Other MarshallSoft Computing products......................29 10.1 The Personal Communications Library for Pascal........29 10.2 The Personal Protocol Library for C...................29 10.3 The Personal Protocol Library for Pascal..............29 PCL4C Users Manual Page 2 1.0 Introduction The Personal Communications Library for the C Language (PCL4C) is an asynchronous communications library designed for experienced software developers programming in C. Four compilers are supported: Microsoft Optimizing C, Microsoft Quick C, Borland Turbo C, and MIX Power C. An IBM PC/XT/AT or compatible is required. The PCL features: o SMALL, COMPACT, MEDIUM & LARGE memory models. o 32 communications and support functions. o Support for the high performance INS16550 UART. o Supports hardware (RTS/CTS) flow control. o Interrupt driven receiver. o Supports 300 baud to 115,200 baud. o Supports COM1, COM2, COM3, and COM4. o Adjustable receive queues from 8 bytes to 32 KB. o Control-BREAK error exit. o 17 communications error conditions trapped. o Allows 2 ports to run concurrently. o Complete modem control & status. o Written in assembly language for small size & high speed. o Terminal program featuring XMODEM, YMODEM, & YMODEM-G. Why should you buy PCL4C ? I can give you several good reasons. COMPLETE - PCL4C is complete since it provides absolute control of the serial ports (including the high performance INS16550). COMPACT - PCL4C is very compact at less than 6 KB. Your application doesn't carry a lot of excess code. FAST - PCL4C is fast since it will run at 38400 baud on even slow 8088 PCs (4.77 MHZ) and at 115200 baud on most everything else. SUPPORT - If you get stuck, you talk to the programmer that wrote the code, not a person hired to answer the phone. BBS - A BBS is available (2400 baud N81) in order to provide immediate support as necessary. NEWSLETTER - One year subscription to the MSC newsletter discusses communications problems and solutions (published quarterly). PRICE - You get PCL4C for a very reasonable price ! UPGRADES - Once you buy PCL4C, you can always update to the most recent version for little more than the cost of sending it out to you. PCL4C Users Manual Page 3 1.1 User Support We want you to be successful in developing your applications using PCL4C! We depend on our customers to let us know what they need in a communications library. This means we are committed to providing the best communications library that we can. If you have any suggestions or comments, please let us know. If you are having a problem using PCL4C, call us at 205-881-4630 between 5 PM and 9 PM CST Monday through Saturday, or FAX us at the same telephone number at any time (24 hours). You can also call at other times and leave a message, and call back later for a reply. You may also call our User Support BBS (2400 baud, no parity, 8 data bits, 1 stop bit) at 205-880-9748 and leave a message (address it to the SYSOP). We will usually have a reply ready for you within 24 hours. The BBS is available 24 hours per day except at 2 PM Sundays for maintenanace. All files are in standard ZIP format. The BBS will contain the latest shareware version of all MarshallSoft products as well as related files such as: BUGS.ZIP -- Bug report. NEWS.ZIP -- Latest news regarding our products. The MarshallSoft Computing, Inc. newsletter "Comm Talk" is published quarterly. It discusses various communications problems and solutions using PCL4C as well as related information. Registered users receive a one year complimentary subscription when first registering and for each update purchased. Of course, you can always write to us. You should receive a reply within a week or so. PCL4C Users Manual Page 4 1.2 A Typical Application In general, there are two classes of applications that use a communications library like PCL4C -- those that use a modem to connect to the outside world and those that connect directly to a peripheral device. In either case, a typical application program using PCL4C might look like the following code outline: ***************************************************** * #include "pcl4c.h" * * * * char Buffer[1024]; * * main() * * {/* initialize serial comm system */ * * SioRxBuf(Port,Buffer,Size1024); * * SioParms(Port,NoParity,OneStopBit,WordLength8); * * SioReset(Port,Baud2400); * * * * ...application code... * * * * /* terminate serial comm system */ * * SioDone(Port); * * } * ***************************************************** In the above example, SioRxBuf is called to set up the a 1024 byte receive buffer; SioParms is called to set up the parity, stop bit count, and word length; SioReset is called to set the baud rate to 2400 and reset the UART (Univeral Asynchronous Receiver / Transmitter). Before leaving your application, SioDone is called to restore the prior state of the serial communications system. If you are using a modem, you also need to be concerned about initializing your modem correctly and handling any required flow control. Refer to the "Talking to Your Modem" chapter for detailed information. PCL4C Users Manual Page 5 1.3 Installation (1) Before installation of PCL4C , your C compiler should already be installed on your system and tested. If you are not familiar with makefiles, refer to your compiler manual. If you are using the interactive environment for Quick C or Turbo C, be sure to compile with the memory model corresponding to the PCL4C library used. Examine the file "FILES.LST" for a list of all the distribution files. (2) Make a backup copy of your distribution disk. Put your original distribution disk in a safe place. (3) Create a work directory on your work disk (normally your harddisk). For example, to create a work directory named PCL4C, we first log onto the work disk and then type: MKDIR PCL4C (4) Copy all the files from your backup copy of the distribution disk to your work directory. For example, to copy from the A: drive to your work directory, we type: CD PCL4C COPY A:*.* (5) [OPTIONAL] Delete the makefiles that you won't need. For example, if you use the Microsoft C compiler, then you want to keep all makefiles ending *._M_ but can delete those for Turbo C (*._T_), Quick C (*._Q_), and MIX Power C (X_*.BAT). You may also delete any libraries that you won't need. (6) Compile SIMPLE.C and link with the appropriate PCL4C library (PCL4C_S.LIB for all but Power C which must use PCL4C_S.MIX). Makefiles (or project files) are provided for each of the supported compilers. a) Microsoft C: Type MAKE SIMPLE._M_ b) Microsoft Quick C: Type MAKE SIMPLE._Q_ c) Borland Turbo C: Type MAKE -FSIMPLE._T_ d) MIX Power C: Type X_SIMPLE SIMPLE.C should compile without any problems as all example code has been tested with each of the supported compilers. (7) The recommended way to test SIMPLE is to run it on two computers connected by a null modem cable. Whatever is typed on one computer should be displayed on the other. PCL4C Users Manual Page 6 2.0 Library Organization The PCL4C library is organized into six categories of functions. Refer to the PCL Reference Manual (PCL4C.REF) for details on individual functions. 2.1 Initialization & Termination There are seven functions in the initialization and termination category. Together, SioParms, SioFIFO, SioRxBuf, and SioReset initialize your serial communications system. Your application must call SioParms and SioRxBuf before calling SioReset, and SioReset must be called before any serial I/O processing can be done. After initialization, SioParms and SioBaud can be called again to change the communications parameters without resetting the serial port. SioFlow can be called to enable hardware flow control. Before exiting from your application, SioDone must be called. Failure to call SioDone can crash your system later. SioRxBuf -- Sets up receive buffer. SioFIFO -- Sets the interrupt level for the INS16550. SioParms -- Sets parity, stop bits, and word length. SioReset -- Initialize a serial port for processing. SioDone -- Terminates further serial processing. SioBaud -- Sets the baud rate of the selected port. SioFlow -- Enables / disables flow control. 2.2 Configuration There are two functions in the configuration category. SioUART is used to change the UART base address for a communications port at a non-standard address, while SioIRQ is used to assign a nonstandard IRQ line to a port. (See the chapter IBM Communications Ports for more details on standard UART addresses and IRQ lines). The configuration category functions should be called before calling SioReset in order to have any effect. There is no "error checking" done, so be very careful in using these functions. SioUART -- Sets the UART base address. SioIRQ -- Assigns an IRQ line to a port. PCL4C Users Manual Page 7 2.3 Modem Control & Status There are seven functions in the modem control and status category which provide your application with complete control over the status and control bits of your modem. There are two modem control bits, "Data Terminal Ready" (DTR) and "Request To Send" (RTS). These bits can be read, set, or cleared by SioDTR and SioRTS. There are four modem status bits, "Data Set Ready" (DSR), "Clear To Send" (CTS), "Ring Indicator" (RI), and "Data Carrier Detect" (DCD). SioModem can read any of the modem status bits. SioDSR, SioCTS, SioRI, and SioDCD can only read their respective modem status bit. Refer to the chapter entitled "RS232 Signals" for a discussion of each of the control and status bits. SioDTR -- Set, clear, or read the Data Terminal Ready (DTR) bit. SioRTS -- Sets, clears, or reads the Request to Send (RTS) line. SioModem -- Reads the modem status register. SioDSR -- Reads the Data Set Ready (DSR) modem status bit. SioCTS -- Reads the Clear to Send (CTS) modem status bit SioDCD -- Reads the Data Carrier Detect (DCD) modem status bit. SioRI -- Reads the Ring Indicator (RI) modem status bit. 2.4 Serial I/O There are six library functions in the serial I/O category. Together, these functions give the programmer complete control over serial I/O. Higher level functions such as protocols and smart modem communications can be completely implemented in terms of these functions. Refer to the example code. SioGetc and SioPutc perform all the actual serial I/O. SioUnGetc and SioRxFlush modify the receive queue. SioLine can be used to test for UART errors. SioGetc -- Reads the next character from the serial line. SioPutc -- Transmit a character over a serial line. SioUnGetc -- "Un-gets" (puts back) a specified character. SioRxFlush -- Flush (clears) the receive buffer. SioRxQue -- Returns the number of characters in the receive queue. SioLine -- Reads the line status register. PCL4C Users Manual Page 8 2.5 Error Detection There are four functions in the error detection category. They are concerned with detecting or reporting communications errors. Use of these functions can make your application significantly more robust. SioBrkKey can be used as an "emergency" exit from your application. SioBrkSig can read or modify the UART break bit. This is useful for signalling the remote system that a fatal condition has occurred. SioLoopBack can be used to test the integrity of your UART. SioError displays a error message corresponding to an error code returned from a PCL4C function (every PCL4C function returns a code). SioBrkKey -- Returns non-zero if the Control-BREAK key was pressed SioBrkSig -- Asserts, cancels, or detects BREAK signal. SioError -- Displays error in text. SioLoopBack -- Performs a UART loopback test. 2.6 General Support There are six functions in the general support category. Strictly speaking, they are not communications functions but are provided in the PCL4C library because they are not always available (especially in some older compiler run-time libraries). At any rate, they take up a very small amount of additional memory. Registered users can also remove these functions from the library if needed. SioInfo -- Returns the library version & memory model. SioCrtWrite -- Write character to the screen. SioDelay -- Delays one or more tics. SioKeyPress -- Detects if keyboard has been pressed. SioKeyRead -- Reads the keyboard. SioTimer -- Returns the number of system clock tics. PCL4C Users Manual Page 9 3.0 Library Organization 3.1 Memory Models Because of the segmented architecture of the INTEL CPU, there are four memory organizations possible for computer programs. These are named the SMALL, COMPACT, MEDIUM, and LARGE memory models, which correspond to the four combinations of "near" and "far" addresses for code and data. Each executable is composed of one or more segments, where each segment can occupy from one byte to 64 KB of memory. A "near" address is a 16 bit offset in a segment, whereas a "far" address consists of both a 16 bit segment value and a 16 bit offset. In the small memory model, code and data each occupy one segment. Thus, near addresses are allocated for both code and data. In the compact memory model, code occupies one segment while data may occupy multiple segments. Near addresses are allocated for code but far addresses are allocated for data. In the medium memory model, data occupies one segment while code may occupy multiple segments. Near addresses are allocated for data but far addresses are allocated for code. In the large memory model, data and code each occupy multiple segments. Far addesses are allocated for both code and data. Thus, both code and data can use as many segments as required. Refer to your compiler manual for a discussion of the memory models supported by your compiler. PCL4C is organized as four separate libraries (PCL4C_S.LIB, PCL4C_C.LIB, PCL4C_M.LIB and PCL4C_L.LIB) corresponding to the four standard memory models. For the MIX Power C compiler, the small, medium, and large models are provided (PCL4C_S.MIX, PCL4C_M.MIX and PCL4C_L.MIX). MIX doesn't support the compact memory model. MODEL CODE DATA Library Small Near Near PCL4C_S.LIB & PCL4C_S.MIX Compact Near Far PCL4C_C.LIB Medium Far Near PCL4C_M.LIB & PCL4C_M.MIX Large Far Far PCL4C_L.LIB & PCL4C_L.MIX However, one can always use the large memory model library PCL4C_L.LIB with any memory model application code by explicitly declaring the PCL4C procedures to be FAR (by prefixing "far" before the name of each function in the PCL4C.H file) and declaring your receive buffer to be FAR. This was the method used in early versions of PCL4C. PCL4C Users Manual Page 10 3.2 Compilers Supported At this time, four C compilers are supported by PCL4C. (1) Microsoft Optimizing C Compiler (2) Microsoft Quick C Compiler (3) Borland Turbo C Compiler (4) MIX Power C Compiler The Microsoft Optimizing C Compiler supports all memory models. Just be careful to link with the PCL4C library that corresponds to the memory model used. Recall that the small memory model is the default. Examine the (small model) makefiles *._M_ for the Microsoft compiler. The Microsoft Quick C Compiler supports all memory models, but be careful to link with the PCL4C library that corresponds with the memory model used. Recall that the small memory model is the default for the command line compiler (QCL) while the medium memory model is the default for the interactive compiler environment. Examine the (small model) makefiles *._Q_ for the Microsoft Quick C compiler. The Borland Turbo C Compiler also supports all memory models. Be sure to link with the correct PCL4C library corresponding to the memory model used. Examine the (small model) makefiles *._T_ for the Turbo C compiler. The MIX Power C Compiler supports the small, medium, and large memory models. However, older versions of Power C only support the small model. Examine the (small model) project batch files X_*.BAT for the Power C Compiler. Other compilers may also work with one or more of the PCL4C libraries but have not been tested. Since registered users have the source code to the library, it should not be difficult to modify PCL4C for use with any MSDOS C compiler. PCL4C Users Manual Page 11 3.3 Using the Library The PCL4C has been tested on a TANDY 1000 (4.77 MHZ 8088 IBM PC clone), a TANDY 3000 (80286 IBM AT clone), a TANDY 1400LT (IBM XT clone), and a Gateway 2000 Cache (25 MHZ 80386-DX). PCL4C has been tested under MSDOS 2.11, 3.2, 3.3, 4.01, and 5.0. Please examine the PCL4C.H file. Note that COM1 is defined as port zero, not port one. The user must assume the responsibilty for passing the correct information when calling PCL4C functions. Note that function prototypes are provided in PCL4C. But since some earlier C compilers don't support function prototypes, PCL4C.H can be modified for no prototypes by changing the line #define PROTOTYPES 1 to #define PROTOTYPES 0 3.4 Example Programs Two communications programs are provided as a demonstration of the PCL4C library -- SIMPLE and TERM. SIMPLE is provided as the simpliest example of communications programming using PCL4C. The user should compile and link SIMPLE.C as a test of the library. If you have two computers, connect them together with a null modem cable and run SIMPLE on both machines. The baud rate in SIMPLE is hard coded to 2400 baud. It is easily changed in the source code. Start SIMPLE by typing SIMPLE followed by the port. For example: SIMPLE 1 Once SIMPLE is started on both computers, whatever is typed on one machine should be displayed on the other, and vice versa. The TERM program is a more capable terminal emulator than SIMPLE. It features modem initialization, hardware flow control, and file transfer using XMODEM, YMODEM, and YMODEM-G communications protocols. TERM can be used to call up any bulletin board system, including the MarshallSoft Computing BBS. Start TERM by typing TERM followed by the port and baud rate. For example: TERM 4 2400 Refer to the chapter "Terminal Emulator Program" for a complete discussion of TERM. PCL4C Users Manual Page 12 3.5 Compiling and Linking Registered users may wish to assemble PCL4C.ASM. Use the /MX switch in order to disable automatic conversion from lower case to upper case. If the /MX switch is not used, then all PCL4C function references in C code must be in upper case. To assemble using the Microsoft assembler: Model Command Small MASM PCL4C /DSMALL_MODEL /MX; Compact MASM PCL4C /DCOMPACT_MODEL /MX; Medium MASM PCL4C /DMEDIUM_MODEL /MX; Large MASM PCL4C /DLARGE_MODEL /MX; To make the (small) model PCL4C.OBJ into a library file: DEL PCL4C_S.LIB LIB PCL4C_S.LIB+PCL4C,PCL4C.MAP; If you are using the MIX Power C Compiler, create the MIX object file (you will need version 1.3 of MIX which has the /_ switch): MIX /_ PCL4C_S Similarly with the other memory model libaries. See the batch files MAKE_S.BAT, MAKE_C.BAT, MAKE_M.BAT, and MAKE_L.BAT. To compile and link (small model) using Microsoft C: cl /AS simple.c /link pcl4c_s.lib To compile and link (small model) using Microsoft Quick C: qcl /AS simple.c /link pcl4c_s.lib To compile and link (small model) using Turbo C: tcc -ms simple.c pcl4c_s.lib To compile and link (small model) using Power C: pc /ms simple.c pcl simple pcl4c_s.mix Makefiles or project files are provided for both SIMPLE and TERM. Turbo C makefiles end with the extension '._T_', Microsoft C makefiles end with '._M_', Microsoft Quick C makefiles files end with '._Q_', and Power C project batch files start with 'X_' and end with '.BAT'. PCL4C Users Manual Page 13 4.0 Talking to Your Modem A modem is used to extend the distance over which you may communicate. Without a modem, your RS232 cable is limited to a maximum of approximately 50 feet. But with a modem, you can communicate literally around the world. 4.1 Modem Standards Two modems can communicate over a telephone line only if they are both using the same signaling frequencies and modulation, which are determined by the the modem standards used. Modem standards can be divided into three sets: (1) speed, (2) data compression used, and (3) error control. The Bell standards (103 & 212A) are those of AT&T. The CCITT (The International Consultative Committee for Telephone and Telegraph) standards are designated as "V. ". Speed Bell 103 -- 300 baud Bell 212A -- 1200 baud V.21 -- 300 baud V.22bis -- 1200 & 2400 baud V.32 -- 4800 & 9600 baud V.32bis -- 4800, 7200, 9600, 12000, and 14400 baud Data Compression MNP 5 -- Microcom Networking Protocol (proprietary). V.42bis -- International data compression standard. Error Control MNP 2,3,4 -- Three level error correction (public domain). V.42 -- International error correction standard. PCL4C Users Manual Page 14 4.2 Flow Control With modems using data compression, the modem to modem connection will run at various speeds depending on the quality of the line. The computer to modem connection will be at a fixed baud rate. Therefore, a protocol (flow control) is necessary to synchronize the data flow between and modems and the computer to modem connection. Refer to your modem manual for information on flow control protocols supported. Two flow control protocols are used by most all modems which require flow control. Software flow control is called "XON/XOFF" (other software flow control character pairs are defined but operate the same as XON/XOFF) and hardware flow control is called "RTS/CTS". Most modems which require flow control enable hardware flow control by default. In XON/XOFF (software) flow control, the computer suspends transmitting data if it receives a XOFF character (13 hex) from the modem, and continues transmitting when it receives a XON character (11 hex). Similiarly, the computer can signal the modem not to send any more data by transmitting a XOFF to it, and can tell the modem to continue transmission be sending a XON. In RTS/CTS (hardware) flow control, the RTS line is used by the computer to signal the modem , while the CTS line is used by the modem to signal the computer. The RTS line is set OFF by the computer to tell the modem to suspend transmission, and set to ON to tell the modem to continue transmission. The CTS line is set to OFF by the modem to tell the computer to stop transmitting, and set to ON to tell the computer to continue transmitting. Given the choice, always choose hardware flow control over software flow control so that all data transmission is transparent. If hardware flow control is not the default (which it almost always is), your should modify your modem initialization string to turn hardware flow control on. Both software and hardware flow control is easy to implement using PCL4C. See TERM_IO.C for an example of hardware flow control. PCL4C Users Manual Page 15 4.3 Modem Initialization If your application uses a modem (as opposed to using a null modem cable), then you should always send an initialization string to your modem if it is a programmable modem such as those made by Hayes. Communication programs such as PROCOMM and TELIX always send such a string automatically as soon as they start up. The particular initialization string depends on the make of your modem. For Hayes and Hayes AT command set compatible modems, the following string (followed by a carriage return) should work: AT E1 S7=60 S11=60 V1 X1 Q0 S0=0 Refer to your Modem User's Guide for a full discussion of these commands. A brief description is as follows: AT Modem attention command. E1 Modem will echo what you send to it. S7=60 Wait 60 seconds for carrier and/or dial tone. S11=60 Use 60 milliseconds for tone dialing duration & spacing. V1 Display result code as words (not numbers). X1 Use the extended result message (CONNECT XXXX) set. Q0 Modem returns result codes. S0=0 Do not answer RING. If your application will answer incoming calls, then set the S0 register to the ring on which to automatically answer. If you send the above codes by using SioPutc (as opposed to typing them from the keyboard), then follow these guidelines: (1) Send an initial carriage return before the initialization string. (2) Pause at least two tics (18 tics to the second) after each character sent as your modem needs the time to perform its own internal processing. Pause a little longer if your modem is not accepting your initialization string. (3) Pause one and a half seconds after sending any initialization command such as ATZ or AT&F since your modem must do quite a bit of processing. If you experience any problems in initializing your Hayes modem, you should first reset it to factory settings by sending: AT&F Refer to the TERM program (functions SendTo and WaitFor in the file MODEM_IO.C) for an example of sending an initialization string to a Hayes compatible modem. PCL4C Users Manual Page 16 5.0 Problems If you cannot get your application to run properly, first compile and run the terminal emulator program TERM provided on your distribution disk. If you are using a null modem cable or a non-programmable modem, be sure to set the HAYES constant to 0 in the source code (#define AT_COMMAND_SET 0). If you are using a Hayes compatible modem, set the AT_COMMAND_SET constant to 1. If you are using a programmable modem which is not Hayes compatible, then you must modify the initialization string for your particular modem. If your application does not run but TERM runs correctly, then you have most likely made a programming mistake in your application. MarshallSoft Computing cannot debug your application, especially over the telephone! However, consider each of the following when searching for an error in your application. 1. Have you included the file PCL4C.H in your application ? 2. Did you link with the correct PCL4C library ? This is the most probable cause if your application 'hangs' as soon as it starts and you must reboot. The function SioInfo() returns the the model ID under which the library was assembled. 3. Is your receive buffer large enough ? If you are using 1K data blocks in YMODEM, then your receive buffer should be at least 1K (2K if baud rates above 19200 are to be used). 4. Have you selected too high a baud rate (if you are using a slow PC) ? If only one COM port is being run, you should be able to run at 38400 baud on 8088 machines and 115200 on most 286 and all 386 and 486 machines. 5. Are you attempting to run another application in the background ? Try running without any other programs running in the background (unload all TSR programs). 6. If you are running two COM ports simultaneously, are you using separate receive buffers ? (you should). 7. Did SioReset return a zero value ? If not, then you must call SioReset again. See TERM.C for an example. 8. Did you send the proper initialization string to your modem ? Did you set DTR and RTS ? (you should). 9. Do you have more than one COM1 port, etc. For example, if you have a COM1 port on your motherboard, you cannot add another COM1 port or modem board that uses COM1 without first disabling the COM1 on the motherboard. PCL4C Users Manual Page 17 6.0 Serial Communications 6.1 Communications Basics The heart of serial communications is the UART (Universal Asynchronous Receiver Transmitter). The IBM PC/XT/AT and compatibles use the INS8250, INS16450, or the INS16550 UART. The purpose of the UART is: (1) To convert bytes from the CPU (Central Processing Unit), into a serial format by adding the necessary start, stop, and parity bits to each byte before transmission, and to then transmit each bit at the correct baud rate. (2) To convert the incoming stream (at a specified baud rate) of serial bits into bytes by removing the start, stop, and parity bits before being made available to the CPU. The UART is part of the serial interface circuitry which allows the CPU to send and receive signals over the RS232 lines. This can be diagrammed as follows: Serial Interface ********************* * * ******* Data Bus * ******** * RS232 Signals * CPU ************** * UART * ****************** ******* * ******** * * * ********************* The INS8250/16450/16550 UART is capable of operating in one of two modes, "polled" and "interrupt driven". The serial communications functions in the BIOS uses the polled method. In this approach, the CPU is typically in a loop asking the UART over and over again if it has a byte ready. If its does, the polling code returns the byte. But, if the next byte comes in before the polling code is executing again, then that byte is lost. In the interrupt driven approach (used by PCL4C for incoming data), when a byte is received by the UART, an "Interrupt Service Routine" (ISR) is executed immediately, suspending temporarily whatever else is executing. The ISR then moves the byte to a buffer so that your application program can later read it. Refer to the sections entitled "RS232 Signals" and "National INS8250 UART" for further information on these topics. PCL4C Users Manual Page 18 6.2 Standard Port Addresses There are a few things to know about how serial communications ports are used by IBM PC/XT/AT and compatible computers. The standard IBM PC/XT/AT configuration values are as follows: Port Reg Base IRQ Line Vector COM1 3F8H 4 12 COM2 2F8H 3 11 COM3 3E8H 4 12 COM4 2E8H 3 11 PCL4C assumes the above values. If necessary, the UART base address can be changed by SioUART, and IRQ lines can be re-assigned by SioIRQ. Refer to the PCL4C Reference Manual for specific details. When installing new communications cards, the following guidelines are recommended: (1) Be sure to read the documentation for the hardware you are installing. Pay special attention to UART base addresses and IRQ lines. (2) If you have a choice in base addresses and IRQ lines, always choose standard values as defined above. (3) The first port should be COM1, the second COM2, etc. (4) Use SioUART to zero all unused ports (for example, call SioUART(COM4,0) if there is no COM4 port installed). (5) Be carefull not to configure two ports for the same address. This is easier to do than you may believe. (6) Choose an external modem over an internal one. It is much easier to debug problems with an external modem than an internal one. (7) Select hardware flow control (RTS/CTS) if flow control is required and hardware flow control is not the default. (8) Always test your port as soon as it is installed. PCL4C Users Manual Page 19 6.3 RS-232 Signals RS-232 is the name of the serial data interface standard used to connect computers to modems. Most IBM compatible computers are built with at least one serial port and use either DB9 (9 pin) or DB25 (25 pin) connectors. A summary of these pins and their function follows. For more detailed information, refer to one of the many books dealing with RS-232 interfacing. Signal Ground Pin 7 (DB25), Pin 5 (DB9) The SG line is used as the common signal ground, and must always be connected. Transmit Data Pin 2 (DB25), Pin 3 (DB9) The TX line is used to carry data from the computer to the modem. Receive Data Pin 3 (DB25), Pin 2 (DB9) The RX line is used to carry data from the modem to the computer. Data Terminal Ready Pin 20 (DB25), Pin 4 (DB9) The DTR line is used by the computer to signal the modem that it is ready. DTR should be set high when talking to a modem. Data Set Ready Pin 6 (DB25), Pin 6 (DB9) The DSR line is used by the modem to signal the computer that it is ready. Request to Send Pin 4 (DB25), Pin 7 (DB9) The RTS line is used to "turn the line around" in half duplex modems, and for hardware flow control in most modems that require flow control. Clear to Send Pin 5 (DB25), Pin 8 (DB9) The CTS line is used to "turn the line around" in half duplex modems, and for hardware flow control in most modems that require flow control. Data Carrier Detect Pin 8 (DB25), Pin 1 (DB9) The DCD line is used by the modem to signal the computer that a data carrier signal is present. Ring Indicator Pin 22 (DB25), Pin 9 (DB9) The RI line is asserted when a 'ring' occurs. PCL4C Users Manual Page 20 6.4 National INS8250, INS16450, and INS16550 UARTs The Personal Communications Library is based on the standard National INS8250, INS16450, and INS16550 UARTs. The 8250 was the original UART used in the IBM PC, whereas the 16450 is a faster version found on most 286 & up machines. The 16550 contains a 16 byte FIFO to further reduce communications overhead. These UARTs consists of 8 register ports as follows: Offset R/W Register 0 R/W Receiver (read) / Transmitter (write) 1 R/W Interrupt Enable (read) 2 R Interrupt Identification 2 W FIFO control (INS16550 only) 3 R/W Data Format (Line Control) 4 R/W RS-232 (Modem) Control 5 R/W Line Status 6 R/W RS-232 (Modem) Status 7 R/W Not used. The UART registers are based at 3F8 (COM1), 2F8 (COM2), 3E8 (COM3), and 2E8 (COM4). COM1 and COM3 share interrupt vector 12 and interrupt request line IRQ4 while COM2 and COM4 share interrupt vector 11 and interrupt request line IRQ3. This means that COM1 and COM3 cannot both be used at the same time. Similarly, COM2 and COM4 cannot both be used at the same time. Port Reg Base IRQ Line Vector COM1 3F8H 4 12 COM2 2F8H 3 11 COM3 3E8H 4 12 COM4 2E8H 3 11 Four sources of interrupts are possible with the 8250 and 16550: (1) receiver error or BREAK, (2) receiver data ready, (3) ready to transmit, and (4) RS232 input. These four sources of interrupts are summarized as follows: Source of Interrupt Action Required to Clear Receiver error or BREAK. Read Line Status register. Receiver data. Read data from data register. Transmitter Buffer Empty. Write to data register or read IID reg. RS232 input. Read Modem Status register. However, PCL4C only enables the receiving data interrupt. This means that interrupts can only be caused by incoming data. If you are not familiar with the INS8250, several good books are available. Refer to the Serial Communications chapter for recommendations. Although a knowledge of the 8250 is not necessary to use PCL4C, a general knowledge of the theory of asynchronous serial communications is recommended. PCL4C Users Manual Page 21 6.5 Register Summary REG 0 : Data Register Reading from the data register fetches the next input byte, once it is ready. Writing to the data register transmits the byte written to it over the serial line. REG 1 : Interrupt Enable The Interrupt Enable register enables each of four types of interrupts when the appropriate bit is set to a one. bit 3 : Enable interrupt on RS232 input. bit 2 : Enable interrupt on receiver error or break. bit 1 : Enable interrupt on transmitter buffer empty (TBE). bit 0 : Enable interrupt on received data (RxRDY). REG 2 : Interrupt Identification (IID) Reading the Interrupt Identification (read only) register once an interrupt has occurred identifies the interrupt as follows: Bit 2 Bit 1 Bit 0 Priority Interrupt 0 0 1 none none 1 1 0 0 (high) Serialization or break. 1 0 0 1 Received data. 0 1 0 2 Transmitter Buffer Empty. 0 0 0 3 (low) RS232 Input. In the INS16650, REG 2 (write only) is also the FIFO control register. Writing bits 6 & 7 will set the FIFO trigger level (number of bytes received before an interrupt is generated). Bit 7 Bit 6 Trigger Bit 7 Bit 6 Trigger 0 0 1 byte 1 1 8 bytes 0 1 4 bytes 1 1 14 bytes REG 3 : Line Control RS232 line parameters are selected by writing to this register. bit 7 : DLAB = 0 bit 6 : BREAK on(1), off(0). bits 5-3: Parity None(000),ODD(001),EVEN(011),MARK(101),SPACE(111) bit 2 : One stop bit(0), two stop bits(1). bits 1-0: Data bits = 5 (00), 6(01), 7(10), 8(11). When the Divisor Latch Access Bit (DLAB) is 1, registers 0 and 1 become the LS and MS bytes of the Baud Rate Divisor registers. Baud Divisor Baud Divisor Baud Divisor 300 0180 4800 0018 38400 0003 1200 0060 9600 000C 57600 0002 2400 0030 19200 0006 115200 0001 PCL4C Users Manual Page 22 REG 4 : Modem Control RTS, DTR, loopback testing, and General Purpose Outputs #1 and #2 are controlled by the Modem Control register as follows: bit 4 : Enable local loopback. bit 3 : Enable GP02. Necessary for 8250 interrupts. bit 2 : Enable GP01. bit 1 : Set / clear RTS. bit 0 : Set / clear DTR. REG 5 : Line Status Reading the Line Status register provides status information as follows (1 for TRUE, 0 for FALSE) : bit 6 : Transmitter Empty. bit 5 : Transmitter Buffer Empty (TBE). bit 4 : BREAK detect. bit 3 : Framing error. bit 2 : Parity error. bit 1 : Overrun error. bit 0 : Data Ready. REG 6 : Modem Status Reading the Modem Status register provides the following status information (1 for TRUE, 0 for FALSE) : bit 7 : DCD status. bit 6 : RI status. bit 5 : DSR status. bit 4 : CTS status. bit 3 : Delta DCD status. bit 2 : Delta RI status. bit 1 : Delta DSR status. bit 0 : Delta CTS status. The delta bits (bits 0 through 3) are set whenever one of the status bits (bits 4 through 7) changes (from 0 to 1 or from 1 to 0) since the last time that the Modem Status register was read. Reading the Modem Status register clear the delta bits. REG 7 : Scratch Register There is no function associated with register 7. It does not exist in early versions of the 8250. PCL4C Users Manual Page 23 7.0 Terminal Emulator Example Program TERM is an communications program suitable for calling up bulletin board systems (BBS) and performing as a PC to PC file copy program. TERM itself is not part of the communications library, but rather it is provided as an example of a communications application using PCL4C. TERM can send a standard Hayes standard AT command set string to your modem. An initialization string is sent by TERM provided that the constant AT_COMMAND_SET in the file TERM.H is defined to be TRUE: #define AT_COMMAND_SET 1 Refer to the chapter "Modem Initialization" for a discussion of initialization strings. TERM also supports hardware flow control (RTS/CTS). Hardware flow control is observed provided that the constant RTS_CTS_CONTROL in the file TERM.H is defined to be TRUE: #define RTS_CTS_CONTROL 1 Refer to the chapter "Flow Control" for a discussion of hardware flow control. TERM can also exchange files using XMODEM, YMODEM (batch capability), and YMODEM-G (streaming YMODEM used with error correcting modems) communications protocols. TERM can accept wildcards in the filename so that multiple files can be sent using YMODEM and YMODEM-G. The protocol timing can also be adjusted (this should not be necessary) by modifying the constants SHORT_WAIT and LONG_WAIT in the TERM.H file. TERM can also be used as a PC to PC transfer program using a null modem cable. In this case, AT_COMMAND_SET and RTS_CTS_CONTROL should be defined to be FALSE in the file TERM.H: #define AT_COMMAND_SET 0 #define RTS_CTS_CONTROL 0 Be advised that most null modem cables are do NOT swap RTS and CTS, which is necessary for hardware flow control. This means that RTS_CTS_CONTROL should never be set to 1 (TRUE) when using a null modem cable unless you are absolutely sure that RTS and CTS are swapped. To start TERM, type TERM followed by the port (1 to 4) and the baud rate (300, 600, 1200, 2400, 4800, 9600, 19200, 38400, 57600, or 115200). For example, to start TERM at 2400 baud on port COM4: TERM 4 2400 The TERM program (but of course not the library itself) is placed in the public domain by MarshallSoft Computing, Inc., and can be used in any way desired by the user. PCL4C Users Manual Page 24 8.0 Legal Issues 8.1 Registration The shareware version of PCL4C.LIB is provided so that you may personally determine the usefulness of the product for yourself. If you can use the Personal Communications Library for C, please register your use with us. Send $45 plus $3 S&H ($6 outside of North America) to: MarshallSoft Computing, Inc. Post Office Box 4543 Huntsville AL 35815 Please pay by check in US dollars drawn on a US bank. Purchase Orders (POs) are accepted from recognized US schools and companies listed in Dunn & Bradstreet. Print the file PCL4C.INV if an invoice is needed. The registered package is mailed first class US Mail (packet air mail overseas). If you are in a hurry, please call us and we can ship immediately within the USA by COD (street address and phone number required). The registered package includes: o Small, Compact, Medium & Large memory model libraries without the shareware screens. o Assembler source code for the library. o Printed Users Manual. o Printed Reference Manual. o Telephone, FAX, and BBS support for one year. o One year subscription (quarterly) to MSC newsletter. o All updates (with printed manuals) are $15 plus $3 S&H ($6 outside of North America). PCL4C.ASM is the source code for the library. The source code is copyrighted by MarshallSoft Computing, Inc. The user is granted a license to use the PCL4C object code in his own application only. PCL4C.ASM is not shareware and may not be sold or given away to anyone. The registered user will receive the latest version of PCL4C by return mail. A 5.25" diskette is provided unless a 3.5" diskette is requested. PCL4C Users Manual Page 25 8.2 License MarshallSoft Computing, Inc. grants the registered user of PCL4C the right to use one copy of the PCL4C library (in object form) on a single computer in the development of any software product without any royalties. The user may not use the library on more than one computer at the same time. The source code for the library (PCL4C.ASM) may not be released in whole or in part. 8.3 Warranty MARSHALLSOFT COMPUTING, INC. DISCLAIMS ALL WARRANTIES RELATING TO THIS SOFTWARE, WHETHER EXPRESSED OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, AND ALL SUCH WARRANTIES ARE EXPRESSLY AND SPECIFICALLY DISCLAIMED. NEITHER MARSHALLSOFT COMPUTING, INC. NOR ANYONE ELSE WHO HAS BEEN INVOLVED IN THE CREATION, PRODUCTION, OR DELIVERY OF THIS SOFTWARE SHALL BE LIABLE FOR ANY INDIRECT, CONSEQUENTIAL, OR INCIDENTAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE SUCH SOFTWARE EVEN IF MARSHALLSOFT COMPUTING, INC. HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES OR CLAIMS. IN NO EVENT SHALL MARSHALLSOFT COMPUTING, INC.'S LIABILITY FOR ANY SUCH DAMAGES EVER EXCEED THE PRICE PAID FOR THE LICENSE TO USE THE SOFTWARE, REGARDLESS OF THE FORM OF THE CLAIM. THE PERSON USING THE SOFTWARE BEARS ALL RISK AS TO THE QUALITY AND PERFORMANCE OF THE SOFTWARE. Some states do not allow the exclusion of the limit of liability for consequential or incidental damages, so the above limitation may not apply to you. This agreement shall be governed by the laws of the State of Alabama and shall inure to the benefit of Marshallsoft Computing, Inc. and any successors, administrators, heirs and assigns. Any action or proceeding brought by either party against the other arising out of or related to this agreement shall be brought only in a STATE or FEDERAL COURT of competent jurisdiction located in Madison County, Alabama. The parties hereby consent to in personam jurisdiction of said courts. PCL4C Users Manual Page 26 9.0 Summary 9.1 Revision History Version 1.0 -- 14 January 1991 -- original release. Version 1.1 -- 11 March 1991 o Added SioUnGetc() function to library. Version 1.2 -- 1 June 1991 o SioParms() bug -- could not call before SioReset. o SioReset() bug -- was not saving & restoring all regs. Version 1.3 -- 1 July 1991 o Added NORESET option to SioReset. o Added SioDSR, SioCTS, SioDCD, SioLoopBack, and SioRI. Version 2.0 -- 1 Nov 1991 o Reorganized as four memory model libraries. o Added SioModel function to library. o Added support for Quick C and Power C. Version 2.1 -- 1 Dec 1991 o Fixed bug due to Microsoft Assembler (MASM 5.0,5.1) error. Version 3.0 -- 15 Jan 1991 o Added SioUART function. o Added "UART undefined" error code. o Added "Bad or missing UART" error code. o Added "Port already enabled" error code. o Added "Cannot enable both COM1 & COM3 ..." error code. o Fixed several minor bugs (using new automated testing). Version 3.1 -- 1 March 1992 o Added SioFIFO (INS16550 support). o Added SioIRQ function. o Increased maximum receive buffer size to 32K bytes. Version 3.2 -- 1 May 1992 o Modified SioReset so that it no longer clears DTR & RTS. o Modified SioModel & renamed to SioInfo. o Fixed bug in SioDone when using 2 ports simultaneously. o Added SioFlow to library. o Added YMODEM-G protocol to TERM program. Version 3.3 -- 3 August 1992 o Fixed bug in SioUnGet when using 2 ports simultaneously. o Add SioRead function. PCL4C Users Manual Page 27 9.2 Function Summary Refer to the PCL4C Reference Manual (PCL4C.REF) for detailed information on the communications and support functions. A one line summary of each function follows: SioBaud Sets the baud rate of the selected port. SioBrkKey Returns non-zero if the Control-BREAK key was pressed. SioBrkSig Asserts, cancels, or detects BREAK signal. SioCrtWrite Write character to the screen. SioCTS Reads the Clear to Send (CTS) modem status bit. SioDCD Reads the Data Carrier Detect (DCD) modem status bit. SioDelay Delays one or more tics (18 tics per second). SioDone Terminates further serial processing. SioDSR Reads the Data Set Ready (DSR) modem status bit. SioDTR Set, clear, or read the Data Terminal Ready (DTR) bit. SioError Displays error in text. SioFIFO Sets the interrupt level for the INS16550. SioFlow Enables / disables hardware flow control. SioGetc Reads the next character from the serial line. SioKeyPress Detects if keyboard has been pressed. SioKeyRead Reads the keyboard. SioInfo Returns library version number & memory model. SioIRQ Assigns an IRQ line to a port. SioLine Reads the line status register. SioLoopBack Performs a UART loopback test. SioModem Reads the modem status register. SioParms Sets parity, stop bits, and word length. SioPutc Transmit a character over a serial line. SioRead Reads any of 7 UART ports. SioReset Initialize a serial port for processing. SioRI Reads the Ring Indicator (RI) modem status bit. SioRTS Sets, clears, or reads the Request to Send (RTS) line. SioRxBuf Sets up receive buffer. SioRxFlush Flushes (clears) the receive buffer. SioRxQue Returns the number of characters in the receive queue. SioTimer Returns the number of system clock tics. SioUART Sets the UART base address. SioUnGetc "Un-gets" (puts back) a specified character. 9.3 Further Reading The best way to learn about serial communications is to read a good book on the subject. Several good texts are available. Two that I like are: (1) C Programmers's Guide to Serial Communications by Joe Campbell (SAMS) (2) Mastering Serial Communications by Peter Gofton (SYBEX). PCL4C Users Manual Page 28 10.0 Other MarshallSoft Computing Products 10.1 The Personal Communications Library for Pascal The Personal Communications Library for Pascal (PCL4P) is a Turbo Pascal version of the Personal Communications Library for C, and is available for $45 plus $3 S&H ($6 S&H overseas). It contains the same library functions, example programs, documentation, and user support. 10.2 The Personal Protocol Library for C The Personal Protocol Library for C (PPL4C) consists of a state driven C language library which implements XMODEM, XMODEM-CRC, XMODEM-1K, XMODEM-G, YMODEM, and YMODEM-G file transfer protocols. This allows the communications application to run two ports simultaneously while interacting with the user at the keyboard. The state drive library functionally emulates background tasking with standard MSDOS. The primary application area for the protocol library is in the development of custom BBS programs (and programs that call BBS's) which require either multiple lines or which require user interaction while a file transfer is underway. The state driven architecture can also be used as a framework and guide to developing customized file transfer protocols. The protocol library (PPL4C) requires the C communications library PCL4C. The PPL4C comes with fully commented C source code, an example program which can transmit or receive two files simultaneously, printed documentation, and one year of telephone, FAX, and BBS support. The Personal Protocol Library for C is available for $35 plus $3 S&H ($6 S&H overseas). It can also be ordered together with the C communications library for $65 for both, plus $3.50 S&H ($7 overseas). 10.3 The Personal Protocol Library for Pascal The Personal Protocol Library for Pascal (PPL4P) is a Turbo Pascal version of the Personal Protocol Library for C, and is available for $35 plus $3 S&H ($6 S&H overseas). It contains the same library functions, example programs, documentation, and user support. The Personal Protocol Library for Pascal is available for $35 plus $3 S&H ($6 S&H overseas). It can also be ordered together with the Pascal communications library for $65 for both, plus $3.50 S&H ($7 overseas). PCL4C Users Manual Page 29