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Thread: any luck with add in serial port cards for xt clones?

  1. Default any luck with add in serial port cards for xt clones?

    Hello, Iv'e tried two different brands of good 8 bit add in serial port cards on my xt clone but neither worked? Anyone know of a particularly compatible card for xt clones?

  2. #2
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    Quote Originally Posted by bob8086 View Post
    Hello, Iv'e tried two different brands of good 8 bit add in serial port cards on my xt clone but neither worked? Anyone know of a particularly compatible card for xt clones?
    Any serial card will work.
    I'd recommend you check the jumper settings on your cards. e.g. you can't have two COM1s, or you maybe the port is disabled.
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  3. Default

    yep, made sure of that before posting, and why the cards don't work is very frustrating!?

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    Questions:
    What is that you're trying to do with the serial card?
    How do you know the card does not work?
    What kind of serial cards? (just serial or multi I/O)?
    Can you post the photos of the cards?

    Some background and troubleshooting info:

    XT clones (normally) will not display whether a serial card is installed or not. The BIOS will silently detect serial ports, and update the following BIOS area locations: 0040:0000, 0040:0002, 0040:0004, 0040:0006 with the base I/O addresses of the detected UARTs, and 0040:0011 bits 3:1 with the number of serial ports detected. You can try using DEBUG to check the data there.

    The serial communication software can use the BIOS information above to determine the presence of the UARTs, and/or INT 14h BIOS services, or auto-detect or allow user to configure the addresses of the UARTs. It is also fairly common not to use BIOS INT 14h services.

    One pitfall, fairly common back in the day, was the interrupt sharing / interrupt configuration. If you have multiple serial ports and your software uses interrupt driven I/O, the best idea is to configure a dedicated IRQ line for each serial port. Simply configuring two ISA devices on the same IRQ line will not work. Some multi-port serial cards allowed using a single IRQ, but IMHO they required some support on the software side to deal with the interrupt sharing. There are some "defaults" applications might use, for example: COM1/IRQ4, COM2/IRQ3, COM3/IRQ4, COM4/IRQ3. As I stated above, these defaults most likely will not work if you have two serial ports sitting on the same IRQ.

    Another possible problem area is the cable wiring and the handshake (RTS/CTS, DTR/DSR, CD). In case of a null-modem connection, it is usually preferable to have a full null-modem cable (not just 3-wire cable with GND/RX/TX), and even if using 3-wire cable, it might be helpful to loop-back RTS to CTS and DTR to DSR and CD on both ends.

  5. Default

    Quote Originally Posted by sergey View Post
    Questions:
    What is that you're trying to do with the serial card?
    How do you know the card does not work?
    What kind of serial cards? (just serial or multi I/O)?
    Can you post the photos of the cards?

    Some background and troubleshooting info:

    XT clones (normally) will not display whether a serial card is installed or not. The BIOS will silently detect serial ports, and update the following BIOS area locations: 0040:0000, 0040:0002, 0040:0004, 0040:0006 with the base I/O addresses of the detected UARTs, and 0040:0011 bits 3:1 with the number of serial ports detected. You can try using DEBUG to check the data there.

    The serial communication software can use the BIOS information above to determine the presence of the UARTs, and/or INT 14h BIOS services, or auto-detect or allow user to configure the addresses of the UARTs. It is also fairly common not to use BIOS INT 14h services.

    One pitfall, fairly common back in the day, was the interrupt sharing / interrupt configuration. If you have multiple serial ports and your software uses interrupt driven I/O, the best idea is to configure a dedicated IRQ line for each serial port. Simply configuring two ISA devices on the same IRQ line will not work. Some multi-port serial cards allowed using a single IRQ, but IMHO they required some support on the software side to deal with the interrupt sharing. There are some "defaults" applications might use, for example: COM1/IRQ4, COM2/IRQ3, COM3/IRQ4, COM4/IRQ3. As I stated above, these defaults most likely will not work if you have two serial ports sitting on the same IRQ.

    Another possible problem area is the cable wiring and the handshake (RTS/CTS, DTR/DSR, CD). In case of a null-modem connection, it is usually preferable to have a full null-modem cable (not just 3-wire cable with GND/RX/TX), and even if using 3-wire cable, it might be helpful to loop-back RTS to CTS and DTR to DSR and CD on both ends.
    Thanks for all the info! I'm trying to use a serial mouse on com1 or com 2. Machine (At&t pc-6300 which I have two of) came with com1 which no longer works so I tried com2 irq3 with add in card but that doesn't want to work either. I have Norton 5 and Qram manifest to look around with as you are suggesting, and have done so in a basic way.

    I know for sure that one of the cards is good via use on an AT motherboard, I will run same tests with second card which as far as I know is good.
    Will get back here when i can, Bob

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    Since the onboard serial port also doesn't work, maybe you have a motherboard problem?
    PCjr, DTK PC-XT Turbo, 386DX 33, 486 laptop, Pentium 120, Pentium III 500, various old laptops, Commodore Colt, all working. I also have a 286 that I need to see if I can repair.

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    This is unfortunately my guess as well. 6300's have a barrel battery that leak, and they've been known to take out motherboards/systems that have been stored in any orientation other than upright.
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  8. Default

    that is a fair guess but it didn't happen on my machines. (I also removed the old batteries and put in a little plastic covered 3.0v pack)

    what is maddening is that my Ctmouse driver shows loaded during boot and then also in a memory read out, yet there is no response in software?!
    And prayers and cursing do not help either

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    I seem to recall that the 6300 can be dip switch set to operate with one of two different serial controllers. Are you certain that you have configured it to the correct onboard one? Additionally do you have the little utility that displays the systems current configuration. An internally stuck dip switch can prevent various settings from actually working.
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  10. Default

    Thanks, the dip switch is set correctly...but that is a good idea to move it back and forth a few times, or even try the wrong position per the onboard related chip since nothing else has worked. (norton 5 sysinfo and qram manifest shows that the port is there.

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