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29444RE: [midatlanticretro] [Semi-OT] Dot Matrix Printer Help

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  • Kelly D. Leavitt
    Feb 25, 2013
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      > RS-232 is still very confusing to me. I've got a Northstar Horizon that can
      > use one type of cable to interface with a terminal or my USB-serial
      > adapter, but my Data I/O EPROM programmer requires a null modem cable, as
      > does my Tandy 200, if I recall. I've tried the null modem cable with the
      > printer and was getting garbage characters, which tells me I'm on the right
      > track, I suppose.

      I think a lot of the old Sperry/Unisys stuff was 7-bit even parity. That might be what the printer is expecting for serial data.

      Try setting the comm port to that if you can and send it data again using the null modem cable.

      Serial is "simple" in some respects in that it is mostly understandable, and slow enough to troubleshoot a bit with an inexpensive scope. rx on one end goes to tx on the other. There are two basic types of devices DTE and DCE. DTE devices are meant to connect to DCE devices, the null modem converts one end from one flavor to another. See http://en.wikipedia.org/wiki/Data_terminal_equipment for some background. Handshaking gets a bit bothersome sometimes, but us usually understandable.

      Don't expect too much data back from the printer other than handshaking. Serial printers were typically bit consumers not bit producers.
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