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Thread: Lab PDP-8/a runninig.

  1. #1

    Default Lab PDP-8/a runninig.

    I got my lab pdp-8/a computer the other day. I had several of these 10 slot boxes that originally came with the G8016 regulator. I thought it was nice to have a light and easy to handle lab omnibus machine for testing various boards. The 5 Chinese PSUs gives+5V, +15V, -15V, -5V and +20V, Had to modify a 24V supply to get down to 20V.

    https://youtu.be/gi13CA1NYpY

    At first it didn't behave very well, but it turned out to be a cable that wasn't seated correctly. Then it would run a simple test program that just increments the AC.

    But what is the nest way of getting various diagnostics into he machine? Since I have been in PDP-11 mode for quite some time I have been used to have PDP11GUI around to download a diagnostic. What is the preferred way of doing it on the PDP-8?

    RIM loader, BIN Loader and a virtual paper tape of a laptop? How to deal with the READER RUN signal?

  2. #2

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    I always used the "sendtape" program that is part of Dave Gesswein's Dumprest package. Easy way to send a paper tape image to the 8.

  3. #3
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    Quote Originally Posted by MattisLind View Post
    RIM loader, BIN Loader and a virtual paper tape of a laptop? How to deal with the READER RUN signal?
    I have run the RIM and BIN loaders on 38kb serial ports without needing the READER RUN signal.
    We did need the READER RUN signal to load a program into FOCAL.
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    Take a look at Lyle Bickley's gtty, a light-weight tty emulator for the Family of 8 that implements software "pacing" to emulate reader-run tape control.

    http://www.computerarium.org/doku/doku.php?id=gtty

  5. #5

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    Quote Originally Posted by jackrubin View Post
    Take a look at Lyle Bickley's gtty, a light-weight tty emulator for the Family of 8 that implements software "pacing" to emulate reader-run tape control.

    http://www.computerarium.org/doku/doku.php?id=gtty
    Thanks!

    To summarize:

    1. Use David Gesswein's sendtape tool.
    2. Use any terminal emulator with file upload since READER RUN is only needed for FOCAL (and BASIC I guess)
    3. Use GTTY as it has software pacing.

    Will look into both sendtape and GTTY. Software pacing sounds interesting.

    If one would like to use the READER RUN signal, how would it work? Connecting it to the DTR or CTS pin to allow flow control?

    I have been contemplating the idea of having some kind of hardware that interfaces Omnibus and give full access to memory and peripherals from an external host. Accessing memory should be possible exactly how the standard front panel do it. But what about peripherals? Would it be possible to generate the required Omnibus signals to mimic the way the CPU execute the IOTs?

    If not peripheral IO is feasible, just to be able to store a file into memory and do standard panel operations (starting, stopping, singlestepping) from a remote host could be useful.

    Or has someone done this already? Don't really want to reinvent the wheel.

  6. #6

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    Rolands extended bootloader board is a start: http://www.vcfed.org/forum/showthrea...-in-PDP-style-!

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    Quote Originally Posted by MattisLind View Post
    If one would like to use the READER RUN signal, how would it work? Connecting it to the DTR or CTS pin to allow flow control?
    Warren't Current Loop to RS-232 adapter connects Reader Run to the CTS pin, and then we enable RTS/CTS flow control on the terminal emulator.
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    Lyle describes tying CTS to the Reader Run flipflop in the notes to GTTY:

    "When running programs like the RIM or BIN loaders, the PDP-8/E is easily able to "keep up" reading a paper tape file from GTTY. However, some programs such as FOCAL, read the paper tape reader slowly. Without hardware modifications, GTTY will attempt to "cram" characters to the PDP-8 when it isn't capable of reading them - hence missed data.

    "To fix this problem, your M8550 or M8655 TTY console board needs to be modified. The modification essentially ties RTS/DTR (CTS after a full handshake null modem)to the Reader Run flip flop on the console board. GTTY is able to sense CTS and wait until Reader Run is set (CTS O.K.) before sending a character to the PDP-8."

    Check out his info file for full details on simple modifications to the M8650/8655 console boards to implement this.

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