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Text File | 1994-10-25 | 24.3 KB | 505 lines

Copy(c)right 1986,1994 by Gary Raymond, New Orleans, La. Port Modem Register Test Program V1.1 Gary Raymond POB 8184 New Orleans, La. 70182 (504) 288-6550 Compuserve 70613,3165 Files Provided: ==================================================================== TESTPORT.COM Serial Port Test Utility. TESTPORT.DOC This document. TestPort will run on just about any version of DOS and with any amount of RAM. If nothing else, TestPort will assist you in learning more about serial communications and understanding your modem. Having written and supported several terminal programs over the past seven years, I have long ago realized that most problems involving terminal software are actually modem or modem configuration problems. This utility should take some of the mystery away from configuring, understanding, and diagnosing serial communications hardware. If for no other reason than curiosity, you owe it to your modem to use TestPort at least once and read through this file. ==================================================================== TestPort is a basic, easy to use, modem diagnostic tool. Although the information TestPort provides will at first be seemingly cryptic to the novice user, it can easily be learned and put to good use. Bit mapping the modem registers provides a wealth of information about the state of your modem. Your modem is both configured and monitored through these registers or electronic switches. Everything from baud rate to data parity is determined by the one (on) or zero (off) bit settings in these registers. Particular register bits are also used to inform the terminal program that a character has arrived or is ready to be transmitted along with numerous other useful information. According to the IBM scheme of things, you could have as many as 65,536 port addresses. These ports have an address in the hardware set up according to IBM's scheme. Each address points to a one byte location called a base address. Since we can both set and retrieve bits in these bytes we refer to them as maskable base registers. Each of the next subsequent nine bytes (BASE+1, BASE+2 etc) form that ports general register set as outlined in the text below. Serial communication ports begin with COM Port number one (COM1) with an address assigned by IBM as decimal 1016 or 3F8 hex. Hence, the address for the COM1 port register is 3F8. This is the place where a byte of data is received (3F8 - Received Data Register) or sent (3F8 - Transmitter Holding Register) depending on requirements at the moment. Therefore the base address allows indirect access to both the THR and RDR (plus BRDL when bit 7 of LCR is set). The next register (the IER) is located at this base address plus one, (3F8 + 1 = 3F9) and so on. There are two general methods of obtaining bytes of data from a serial port after it has been set up. The first involves stopping every so often and looking to see if a byte has arrived, and if so, taking it. This method of polling the modem registers is ok when working at very slow baud rates. Polling is the method used by the PC's Basic Input Output Service (BIOS firmware.) Unfortunately, if a byte of data arrives before we have had a change to remove the previous one, information can be lost. To overcome this drawback of polling we can force the PC to react to the arrival of a byte by removing and saving it in a special storage area until we have time to use it. This is done by designing a special Interrupt Service Routine (ISR) that will be activated instantly (no matter what else the PC may be doing) to collect and store the byte of data. This is referred to as an "interrupt on receive" terminal program, such as our product, SLICK terminal. There are many things that can go wrong when installing a modem on your computer. Usually, problems are evenly divided between hardware and software configuration errors. In general, the modem itself must be mechanically set, via jumper pins or dip switches, to address whatever available serial port is usable on your PC. The selected port must also be paired with an interrupt request line (IRQ). Note, no two serial devices (examp: modem and mouse) may share actively the same serial port IRQ address. Some modems force, or allow you to force, certain register bits either high (1) or low (0) in lieu of preferred software control. TestPort is useful in EXAMINING all of the register settings that occur as a results of these various configurations. Improper configuration of software is another problem. Here, there are generally three areas of trouble. Improper comm port, interrupt and modem command (initialization) string settings. So, to review, One: the serial services must first be available on the PC. Two: both the modem and terminal software must agree in settings with the PC hardware you are attempting to access. And finally, the modem initialization command string must correctly complete the job of setting any other registers that require attention, such as setting FAX mode on or off, hardware error correction enabled or disabled, etc. etc. For what its worth, just one wrong AT command in the string will cause the entire string to FAIL. So, if your particular brand modem does not use &D1 (set dtr) as an example, and, it is inserted into your complete string, such as ATM1S0=0V1X4&D1S7=45, then the entire string will fail returning an error message, leaving your modem still waiting to be configured. ==================================================================== USING TestPort's register mapping ability: To run TestPort with mapping action, you must pass the active port number via a command parameter. TestPort will work on the four standard IBM default ports of 1 (3F8), 2 (2F8), 3 (3E8), and 4 (2E8). Let's assume your modem is configured to operate using COM2. Type TESTPORT 2 at the DOS prompt. In most cases, you will really want to do this while your terminal program is active. You do this by dropping to DOS from within your terminal program, then executing TestPort. Most all Terminal programs have a drop to DOS feature, although it might be called something else. TestPort does a passive read only on these registers and therefore will in no way alter or change their bit settings. By using the drop to dos feature, which allows the modem code to remain loaded in ram, you eliminate the possibility that any modem registers will be inadvertently altered, by your terminal program, before you get to read the registers. Some terminal programs also have features that allow the naming and execution of any external dos utility via a combination of trigger hot keys. This is a MUCH better way of quickly running TestPort. Don't forget in either case to pass the active port number in use. (i.e. TESTPORT 2.) If TestPort is executed as an external utility, screen output data will remain until a key is pressed. This will give you opportunity to hit Shft PrtSc and save a copy of the screen to your printer for evaluation and analysis. If you do not have a printer, you should make a long hand record on paper. USING TestPort's UART finder: Running TestPort without a port parameter will cause TestPort to cycle through the four common UART addresses looking for an active (U)niversal (A)synchronous (C)ommunications (C)ontroller. (8250 IC) If active port addresses are located, TestPort will notify you of those that appeared active. Notice, I said appeared active. It is possible to have two serial ports but only one terminated to a modem. The other may be just a jack on the rear of your PC, there for some later expansion. A simple serial card with its open jack will still show as an active port. Screen Output: ------------------------------------------------------------------------ The Correct Syntax is TESTPORT #, (# to test), i.e. TESTPORT 4, however, TestPort will now try to determine what if any serial port is responding to TestPort's Inquiries.................... COM1 appears to have an active UART! COM2 appears to be inactive. COM3 appears to be inactive. COM4 appears to have an active UART! Enter Port# to test or Esc to exit -> In five seconds type AT <Enter>, active port will echo OK or 0, else Esc! ------------------------------------------------------------------------ Although this kind of information is by far un-conclusive, it does give you enough insights to continue experimenting. In the case of the information given above, the modem must be attached to either COM1 or COM4. To determine which it is, try entering 1 first. If there is no echoing of your keystroke or an OK reply to AT (the modem attention command) the probability is COM1 is not the port connected to your modem. Now try 4. This should test ok! More than likely, COM1 is an extra, as of yet unused, serial adapter. Although this testing facility is only a raw polling terminal, set to 1200 baud, N81, it can easily be used for simple task, like dialing out to test other modems etc. Try typing ATH1 and see if you hear your modem take the line off hook....ATH0 to replace it. Fun hun? ==================================================================== SCREEN GENERATED BY TESTPORT when mapping registers: When TestPort is run, it produces the following screen, indicating the various one byte registers that have been read, their decimal, hex, and (binary) bit map values. It's those bit settings you are most interested in. The two indirect registers (THR and RDR) read via the base register are not useful here. However, those two plus the eight indicated account for the 10 registers of a UART chip. ******************************************************* Modem Register Bit Map by Gary Raymond Phone (504) 288-6550 Modem Registers Dec Value Hex Value Bit Map 76543210 IER (Int Enable) 0 00 00000000 IIR (Int ID) 1 01 00000001 LCR (Line Control) 3 03 00000011 MCR (Modem Cont) 8 08 00001000 LSR (Line Status) 97 61 01100001 MSR (Modem Status) 48 30 00110000 BRDL (Low Register) 6 06 00000110 BRDH (Hi Register) 0 00 00000000 ******************************************************* Hit Any Key to Exit! NOTE: Bit positions are read left to right, starting with position 0 (zero) and ending with 7. This accounts for a full byte of eight bits. ==================================================================== SAMPLE USES for TESTPORT: Q) My modem wont hang up, what do I look for? A) Look at bits 0 and 1 of MCR after starting your terminal program but before dialing a number. They should both be set to 1. If not check to see if your modem requires external dip switch settings to force DTR, RTS or software AT commands like &D2 and &C1. Q) How can I tell if my terminal program is interrupt driven or a polling BIOS type? A) Look at bit 0 of IER, it will be set to 1 if the terminal is interrupt driven. Also, bit 3 of MCR is usually set to 1 as well. These bits are set to 0 (zero) in a polling terminal. Q) My modem wont respond on COM2. A) Run TESTPORT 2. If If you see each modem register returning FF hex (dec 255 or 11111111 binary) odds are this port is not activated correctly via pin or dip settings on the modem card. Check your modem manual for correct pin or dip switch settings. Q) How can I tell what Baud rate my modem is locked at? A) First, run TestPort and obtain the BRDL and BRDH register values. Then cross reference them with the Baud Rate Value chart in this document file. Q) Can I use TestPort to place a call to a BBS? A) Yes, but it's VERY limited as a polling terminal and not intended for that kind of application. No protocols, no dial directory, no no nothing, just a bare foot terminal! Q) My modem and software configured for COM3 is brain dead, can TestPort help? A) You bet! Some serial communications software, especially tsr type, use BIOS services for communicating with the serial ports. BIOS then depends on DOS to insert the correct port addresses into the BIOS area of memory. Some versions of DOS fail to place the default addresses for COM3 and COM4 in the required BIOS area of memory. TestPort overcomes this limitation by poking ALL of the IBM default addresses (3F8 - 2F8 - 3E8 - 2E8) into the correct area of bios memory starting at segment 0040. This feature is automatic anytime you run TestPort in any mode. To cancel out these values, you only need reboot the PC. I will also provide a seperate utility (PCA.COM) that can be used via your autoexec.bat to insure these addresses are always available after bootup. Q) My terminal program has a host mode that allows remote access to DOS via a redirection statement in a batch file. Only guess what? It locks up my computer. Can TestPort help me? A) Well, maybe. There are many computers (clones or otherwise) that just do not take kindly to re-direction. (CTTY COM1 or CTTY > AUX1 type calls) If the reason is due to the problem outlined in the answer above, TestPort or PCA will solve it. If not, there is a device driver in the public domain called GateWay that usually will accept re-direction. It can be found on most BBS'es. One nice thing about GateWay is it still allows access to the host keyboard and monitor; simple re-direction does not. Q) Can I use TestPort to see the default and or active settings of all registers in my modem? A) Yes, actually, you can do that with any terminal program. To use TestPort, type TESTPORT at the dos prompt. Select the active port number and wait five seconds for the terminal to respond. Type AT&V then hit enter. On some older modems you cannot dump the entire register set and you must poll each individually. Say you want to see the present value in S7, type ATS7? and so on. Q) My old modem had a volume control on the card. My new one does not. Can TestPort save my marriage and turn down the volume? A) Yes, and again, it can also be done with your present terminal. By default most modems allow the speaker on at full volume. You can control this by resetting the M and L registers. ATM1 will turn off the sound after a connect and ATL0 will reduce the volume to the lowest setting. Of cource, these switches belong together in your initialization command string. (ATM1L1etc.etc.etc.) ==================================================================== MODEM REGISTER BIT MAP DATA: For general purpose information, the port addresses of these registers are as follows: BASE = COMPORT ADDRESS (COM1 = 3F8h) Therefore, MCR for COM1 equals 3F8h + 4 or 3FCh Ten Modem Registers --------------------------------------------- THR,RDR, *BRDL = BASE IER, *BRDH = BASE + 1 ; Interrupt Enable Register IIR = BASE + 2 ; Interrupt Identification Register LCR = BASE + 3 ; Line Control Register MCR = BASE + 4 ; Modem Control Register LSR = BASE + 5 ; Line Status Register MSR = BASE + 6 ; Modem Satus Register --------------------------------------------- *requires bit 7 set to 1 in LCR for access ==================================================================== IER BIT MAPPING (Interrupt Enable Register) --------------------------------------------- BIT Activates Action 0 = Data Received Read RDR 1 = THR empty Output to THR 2 = Data error/break Read LSR 3 = MSR change Read MSR 4 = zero 5 = zero 6 = zero 7 = zero Although the 8250 Uart has 10 one byte registers, only seven have direct access, and of the seven, three of these are used redundantly to gain access to the three non directly accessible registers. This indirect access is achieved by setting bit 7 of LSR to 1. Then, the BRDL and BRDH registers are accesses at BASE and BASE + 1. These two registers are used to lock the port baud rate. The BRD (Baud Rate Divisor) is a 16 bit number (two bytes) and therefore requires two (one byte) register access through BASE and BASE + 1. Interesting enough, the high byte is only necessary for baud rates of 300 or below. At 1200 or higher BRDH is set at zero. The formula for calculating the BRD value demonstrates why. UART CLOCK SPEED (1.8432mhz) BRD = ---------------------------- 16 x bit transfer rate (not really baud) 1,843,200 BRD = --------- = 256 or 110000000 or 100h 16 x 300 B B R R D D breaking the result into H L two bytes produces = 1 & 1000000 where BRDH = 1hex and BRDL = 80h (128 dec) FOR 1200 BAUD: 1,843,200 BRD = --------- = 96 or 1100000 or 60h 16 x 1200 B B R R D D breaking the result into H L two bytes produces = 0 & 1100000 where BRDH = 0hex and BRDL = 60h (96 dec) The THR (Transmit Holding Register) and RDR (Received Data Register) are accessed via the same physical address as the port base address. Since you cannot in theory send and receive at the same instant, this little scheme seems ok. IIR BIT MAPPING (Interrupt Identification Register) --------------------------------------------- BIT 0 = more than 1 intr has occurred 12 12 1-2 = 00 change in MSR 10 data received 01 THR empty 11 recv error/break 3 = zero 4 = zero 5 = zero 6 = zero 7 = zero LCR BIT MAPPING (Line Control Register) --------------------------------------------- BIT 01 01 01 = Data Length 00=5bits 10=7bits 01=6bits 11=8bits 2 = Stop Bits 0=1bit 1=2bits 345 345 345 = Parity 000=NONE 101=MARK 100=ODD 111=SPACE 110=EVEN 6 = Break Condition 0=disabled 1=enabled 7 = Port Toggle 0=Use THR/RDR/IER 1=Use BRDL/BRDH SAMPLE: Using N parity, 8 data bits and 1 stop bit requires the LCR register of 00000000 to be then set as follows: 76543210 = bit pattern 11 = 8 bits 0 = 1 stop bit 000 = no parity 0 = break disabled 0 = toggle inactive ---------- 00000011 = 3h to send to LCR Bit 7 of LCR controls the dual function of bits 0 and 1 in the IER Register and should be set to zero in the above example. MCR BIT MAPPING (Modem Control Register) --------------------------------------------- BIT 0 = Set DTR line active 1 = Set RTS line active 2 = USER BIT #1 3 = USER BIT #2 4 = UART loopback 5 = zero 6 = zero 7 = zero Bit 3 is normally set to 1 for interrupt driven terminal programs. Most programs force the modem to hang up by setting bits 0 and 1 to 0. Modem software setup for these first two bits therefore is usually 1 and 1. LSR BIT MAPPING (Line Status Register) --------------------------------------------- BIT 0 = byte in RDR (received) 1 = overrun in RDR 2 = Parity error detected 3 = Framing error (out of sync, no stop bit received) 4 = Break Detect 5 = THR empty 6 = TSR empty (removes char from THR) 7 = Time Out A communications program usually checks bit 5 here before sending another character out the base port. MSR BIT MAPPING (Modem Status Register) --------------------------------------------- BIT 0 = change in [C]lear [T]o [S]end CTS 1 = change in [D]ata [S]et [R]eady DSR 2 = change in ring indicator RI 3 = change in [D]ata [C]arrier [D]etect DCD 4 = Clear to send ..... [CTS] set high 5 = Data set ready .... [DSR] set high 6 = Ring Indicator .... [RI] set high 7 = Data Carrier detect [DCD] set high Most BBS programs monitor bit 7 of the MSR to determine if carrier is lost during a logon. =================================================================== BAUD RATE DIVISOR (BRD Register) CHART Bit Rate BRDH BRDL --------------------------------------- 50 09h 00h 110 04h 17h 300 01h 80h --------------------------------------- 1200 00h 60h From 1200 up, BRDH is 2400 00h 30h always set to zero! 4800 00h 18h 9600 00h 0Ch 19200 00h 06h =================================================================== Registering your copy will help continue the competitive advantages of providing economical shareware. As an additional bonus, I will ship you several other useful modem and dos utilities free! If you have any comments or suggestions about this utility, feel free to write or call. Name_____________________________________________________________ Mailing Address__________________________________________________ City & State ___________________________________________________ ZIP _____________________________ Phone _________________________ Send $4 + $1 (ship & hand) check or money order to: Gary Raymond POB 8184 New Orleans, La. 70182 (504) 288-6550 Compuserve 70613,3165 ==================================================================== EOF