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Thread: ASR33 - Starting the tape reade in line mode

  1. #11


    I believe a KSR33 is like an ASR33, but `keyboard only`, IE: No tape reader/punch.
    and a Data Dynamics 390 with tape reader/punch is based on an ASR33

    I have a 390 printer manual (DDTM 025 Issue 3, 1971), which shows that start=auto and so for online reading the lever should be set to `start`
    and Ctrl+Q (DC1) should be sent from the host to start the reader.

    It is stopped by sending Ctrl+S (DC3) or moving the lever away from `start`

    Not sure if this is sensible, but it may be worth checking the parity - it should be set up for `even`, but I think it can be set up for `odd`

    If not something like that, then perhaps some physical fault.
    I am part way through scanning the manual, which is over one inch thick, but won't have time to finish for a few weeks.

  2. #12


    I had completely forgotten about parity. Yes, that could prevent XON from working (if the teletype has that feature enabled). However, I'm not sure if even parity is the answer. Ctrl-Q/XON/DC1 with even parity is the same as "no parity" (8n1). But, if your TTY operates with odd parity, that would matter. I just don't recall received parity mattering, though, at least on the devices I used to use.

    If the odd relay is a "reader run" circuit, then that may be how you have to start the reader. You said there were two wires on the interface that connected to it? What you'd have to determine is whether you short the two wires, apply voltage, or something else. Perhaps some circuit analysis first would be wise.
    - Doug

  3. #13
    Join Date
    Jul 2014
    Rhode Island


    DEC commonly added a small circuit board holding a relay to the ASR33 so they could remotely control the reader. There was an additional 20mA circuit from the computer's serial port that would turn off the reader until the character had been read from the buffer.
    Member of the Rhode Island Computer Museum


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