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Thread: Help with serial interface PC to Sol-20

  1. #1

    Default Help with serial interface PC to Sol-20

    I received my null modem cable setup and tried to establish a working connection between my 486 laptop with 9-pin serial interface and my Sol-20 serial interface, but have failed. My 486 Laptop is an HP Internet advisor workstation. Back a few years ago buying one of these was a cheap way of getting a vintage PC laptop with a 3.5Ē disk drive. Iíve just it successfully to create 720k disks for my vintage HP computers. This PC has many interface ports along with the 9-pin serial interface. It is running Windows 95. Iím not really sure which COM port (COM1, COM2, COM3, etc) the 9-pin aerial port is. Iíve tried them all. I am using Hyperterminal and set the data rate for 1200 and 8-N-1. On my Sol-29 I have entered the SET I=1 command, but when I try to send over the Ďtrain.entí file. Nothing happens. Is there a way to check if I have the COM port number correct on my PC? Also, does anyone have a detailed, step-by-step how-to instructions on how to send an Ď.entí file from a Windows PC to the Sol-20?

  2. #2
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    Simplest way to check is in Hyperterm go "Properties", "Settings" tab "ascii setup" make sure "Echo typed characters" is cleared.
    Then loop pins 2+3 on the serial cable and what you type should be echoed...
    Dave
    G4UGM

    Looking for Analog Computers, Drum Plotters, and Graphics Terminals

  3. #3

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    To test the link use the TERM command on the Sol. And on the SOL type SET I=1 like you have tried. This makes the SOL accept data from the computer, so if you type anything on the computer, it should appear on the SOL's screen.

    Check the Sol switches, S3 - 6 ON & others off in the S3 bank (1200 baud).
    S4-5 off(no parity).
    S4-4 on, 1 stop bit.
    S4-2 and S4-3 are both off (8 bit word length).

    There were some mistakes in the manual related to the 6 or 7 bit selections.

    I have occasionally had to replace damaged transceiver IC's, but these can be checked with the scope fairly easily.

    I also remember now, in my sol the MC1489A receiver IC was defective and I didn't have one in my stock and had to order one. I think these IC's get damaged by the connections to long cables and electrostatic charges in those. Probably it is unlikely your IC is defective though, but maybe worth checking if all seems ok with the wiring, switch and software settings of the hookup.

    One reason I used a real null modem cable, rather than a Null modem adapter, is in the adapters, unlike the cable, they seem to have a lot of wiring variations.
    Last edited by Hugo Holden; September 27th, 2020 at 02:20 PM.

  4. #4
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    You also need to make sure that the Sol's pin 2 is connected to the PC's pin 3 and vice versa somewhere either in the null modem or RS232 cable or you'll have both talking to the wrong pins.
    Crazy old guy with a basement full of Pentium 1 laptops and parts

  5. #5

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    On the 486 PC using Hyperterminal, File, Properties Connect using: Direct to Com 1 and then select Call, Connect yields an pop up window stating that 'Unable to open COM1'. If I select File, Properties Connect using: Com 2 and Select Call, Connect then the timer in the lower lefthand area of the Hyperterminal window starts to count up. In the File, Properties, Settings tab what should the Emulation pull down menu be set to? I have it set to Auto Detect. Also, in the Properties, Port Settings tab where Bits per second: is set to 1200, what should the Flow control pull down menu be set to? I have it set to Hardware.

  6. #6

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    Quote Originally Posted by Old_hitech View Post
    Also, does anyone have a detailed, step-by-step how-to instructions on how to send an ‘.ent’ file from a Windows PC to the Sol-20?
    If you were running TeraTerm (the one I use) I could give an exact list of of steps I do to transfer a .ent file to the Sol. I have not tried hyperterminal, so I'm not sure how well the instruction list would suit it.

  7. #7

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    Hugo, believe me I am running out of patience with my Hyperterminal setup. So I looked briefly into using TeraTerm as I have my son's hand-me-down HP laptop running Windows 10. It has USB and HDMI and Ethernet ports, but no classic 9-pin or 25-pin serial port connectors. Maybe I could use a USB to 9-pin serial port adapter?
    I did check my 9-pin to 25-pin cable connections and pin 2 and pin 3 are swapped in a null modem configuration. I also checked my Sol-20 serial interface switch settings and I now have them as you described. I need to check if the 486 PC serial port is actually outputting a signal with the COM port I have selected in Hyperterminal. I will bring out my oscilloscope and check this later this evening or tomorrow.
    All this effort to get a disk drive setup on my Sol-20 with the ability to load and save BASIC programs is making me want to bring out my cassette recorder....

  8. #8

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    Quote Originally Posted by Old_hitech View Post
    I did check my 9-pin to 25-pin cable connections and pin 2 and pin 3 are swapped in a null modem configuration
    Don't forget there are two crossings in the Null modem cable, the Tx and Rx pins 2 & 3 are crossed, but so are the RTS and CTS connections, so check those too.

    I also have one of these permanently plugged in my linkup which helps when something goes wrong:

    https://www.ebay.com/itm/RS232-DB25-...IAAOSwQYZWznBE

  9. #9
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    Quote Originally Posted by Hugo Holden View Post
    Don't forget there are two crossings in the Null modem cable, the Tx and Rx pins 2 & 3 are crossed, but so are the RTS and CTS connections, so check those too.
    With a null-modem cable going from a DE9 to a DB25 don't cross pins 2 and 3, they're already swapped. Double check your cable and check device manager to make sure that your com port is properly enabled.

    See:
    https://en.wikipedia.org/wiki/Null_modem

    Nothing wrong with Hyperterm as long as you're connecting to a valid com port; it doesn't have as many options as PuTTY or Teraterm etc., but some see that as a plus

    As mentioned above, disconnect the cable, turn off local echo and jumper pin 2 to pin 3; what you type should appear on the screen and stop when you remove the jumper.
    Last edited by MikeS; September 27th, 2020 at 08:07 PM.

  10. #10

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    I used my oscilloscope on the 9-pin serial port on pins 2 and 3 at different times and I see a constant distorted 17ms sine wave. I tried using selecting COM2 and COM3 (COM1 and COM4 gave an error) and sending the 'train.ent' file and did not see any difference in activity on pins 2 or 3. I do not think I am correctly selecting the 9-pin serial port, but not sure how this can be done. I going to throw in the towel on using my 486 PC and try a more modern approach using a Windows 10 laptop running Teraterm and USB to 9-pin serial connector adapter. Can anyone recommend a USB to 9-pin serial adapter?

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