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Thread: VT320 problems

  1. #1

    Default VT320 problems

    Now that I have my 11/23+ system running I wanted to try using a real DEC terminal. Connected a VT320 to the computer and all the boot up information appeared on the screen. However, when I went to respond the terminal is apparently not sending to the computer. I have the cable from the terminal plugged into a H8575-A adapter which is then connected to the Dbit cable going to the RS-232 port on the CPU board. I tried connecting pin 2 to 3 on the H8975 but got nothing on the screen. I ran through the loopback tests suggested for the terminal and end up with the VT320 DEC-423 Port Error -- 5. Also tried the printer port and got Error 6. So apparently I only have one way communication - computer to terminal. Anyone have further test suggestions or a possible fix? Or am I just out of luck with this particular terminal?

    Thank you for any ideas.

    Al

  2. #2

    Default

    turn off hardware handshaking on the terminal?
    Member of the Rhode Island Computer Museum
    http://www.ricomputermuseum.org

  3. #3

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    It is set up for DEC-423, Data Leads Only

  4. #4
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    Default

    check rs232/rs422. Set term to vt102 or lowest possible type...
    Dave
    G4UGM

    Looking for Analog Computers, Drum Plotters, and Graphics Terminals

  5. #5

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    What kind of cable do you have? Often missing CTS/CD/DSR signals (provided by 'real' modems) will prevent sending. Null modem cables will fake these signals. We used to use 3-wire cables between DEC cpu's and serial terminals, which with a 25pin connector required jumpering pins 4->5 and 6->8->20 at both ends of the cable, as well as crossing pins 2-3 between the two ends of the cable.

  6. #6

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    Check the number of data bits and the parity mode. The terminal will probably be a bit more lenient about characters it receives, but the monitor/OS may be very picky. Try 7 data bits, 1 stop bit and vary the parity. I'd try mark parity then odd, even, etc.

  7. #7

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    Here are some clarifications on my connections between the VT320 and my 11/23+ system. The terminal only has DEC-423 connectors, no DB25. The attached documents show the pin assignments for the 6-pin DEC-423 connector, the cable used and the adapter to go from DEC-423 to DB25. The adapter then connects to the DB25 connector on the serial port of the computer. MMJ jack pin assignment.docMMJ crossover cable.docMMJ adapter.doc

  8. #8
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    Quote Originally Posted by lsi11al View Post
    Here are some clarifications on my connections between the VT320 and my 11/23+ system. The terminal only has DEC-423 connectors, no DB25. The attached documents show the pin assignments for the 6-pin DEC-423 connector, the cable used and the adapter to go from DEC-423 to DB25. The adapter then connects to the DB25 connector on the serial port of the computer. MMJ jack pin assignment.docMMJ crossover cable.docMMJ adapter.doc
    And when you loop 2 to 3 on the 25pin you get nothing when you type? Is HOLD pressed on the terminal? Is RX and RX baud rate the same?
    Dave
    G4UGM

    Looking for Analog Computers, Drum Plotters, and Graphics Terminals

  9. #9

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    HOLD is not pressed, RX and TX baud rates are the same and I get nothing on screen when I type.

  10. #10

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    Received a female 6 pin connector today and wired it as complete loop back connector and ran the loopback tests as per the VT320 Pocket Service Guide. Both the communications port and the printer port result in errors. So input to the terminal from the computer works but output to either the computer or the printer port does not. At this point unless someone can point to something I am overlooking I am thinking that there is an internal problem on the control board. Given the directionality symptoms can anyone suggest what chip or chips might be at fault. Also welcome any thoughts on whether this is worthwhile to pursue.

    Thank you.

    Al

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