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31073Re: [midatlanticretro] Re: CP/M CBIOS LST question

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  • Brian Schenkenberger, VAXman-
    Jun 1, 2013
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      Dave McGuire <Mcguire@...> writes:

      >On 06/01/2013 09:17 AM, joshbensadon wrote:
      >> I save a lot of time with RS-232 by using an LED Tester. It has male
      >> & female DB connectors and plugs in line to show which lines are
      >> being driven. Connect it to one side first and observe the TX led is
      >> on, then unplug and connect to the other side and observe the RX led
      >> is on. If both show TX (or RX) led's on, then you need a NULL (or
      >> undo a NULL?).
      >>
      >> I highly recommend you get an 18 LED tester. There are some 9 LED
      >> testers that use bi-colour LED's. These suck as you can't see the
      >> data pulses unless you have a very keen eye for colour changes (which
      >> I don't).
      >
      > I'm sorry but I have to disagree here. 99% of RS232 troubleshooting
      >involves looking at the static states of signals, not looking for fast
      >transitions due to character transfer on the TxD and RxD lines. As long
      >as one end is driving TxD and the other end is driving RxD, your data
      >lines will be fine. (wiring-wise)
      >
      > That said, though, if a different one works better for you, more power
      >to you. But my own opinion is that the nine-LED ones are far from
      >useless; in fact they're all I use anymore.
      >
      > Either way, though, something to indicate the states of the lines is
      >indispensable for RS232 interfacing. They're so cheap and so necessary
      >that there's really no excuse for not having one.

      Wow. Apparently, one can still buy the breakout box model I have had for
      probably 2 decades or more:

      http://www.plccenter.com/en-US/Buy/GC%20ELECTRONICS/43088

      It HAS BEEN indispensable over the years!

      --
      VAXman- A Bored Certified VMS Kernel Mode Hacker VAXman(at)TMESIS(dot)ORG

      Well I speak to machines with the voice of humanity.
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