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Re: Help on 5 wire mod not working

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  • ZipItPet
    ... Sounds like a low voltage signal (assuming no wiring errors) It looks like one direction is working (PC- Zipit). The bootstrap program that runs on the
    Message 1 of 4 , Jul 18, 2008
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      --- In zipitwireless@yahoogroups.com, "David" <kd7nzk@...> wrote:
      Sounds like a low voltage signal (assuming no wiring errors)
      It looks like one direction is working (PC->Zipit).

      The bootstrap program that runs on the ZipitV1 starts with
      "ZPM .02 - 57.6Kbps new cmds" (see source in ZPM.A)

      You are getting corrupted data going the other way Zipit->PC
      (but the fact it is printing anything indicates the PC->Zipit is good)
      > $b9$$d5$$83$.02 - 57.6Kbps new c$ed$ds$0e$
      > $0e$$cf$K@>$0e$$0e$$9f$#$e1$cMD ES1$0f$$0b$OK

      ------
      IIRC the voltage on the MAX chip should be 3.5V

      BUT the Max233A chip is officially a 5V chip. If you run it at 3.5V
      the signals won't be official RS-232 levels, but in my experience it
      works good enough for most RS-232 ports.

      BTW: it varies depending on the MAX chip.
      BTW: each RS-232/COM port has slightly different voltage thresholds
      on incoming data

      ------
      Advice:
      #1) if you have them available, swap in another MAX-233A chip, cross
      your fingers and try again

      #2) if that doesn't work, power the MAX-233A chip with 5V. This will
      pump up the RS-232 signal levels to official levels.
      BUT the Zipit RXD signals will be too high (swinging between 0V and
      ~5V). You should add a level shifter (eg: something as simple as a
      two resistor voltage divider).
      NOTE: The Zipit TXD signal will be fine.


      Good luck
    • David
      In case anyone else runs into the same problem, it seems the pinout for the MAX233A DIP package and the MAX233 SO package is NOT the same. I followed the
      Message 2 of 4 , Aug 13, 2008
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        In case anyone else runs into the same problem, it seems the pinout
        for the MAX233A DIP package and the MAX233 SO package is NOT the same.
        I followed the pinout on the elinux wiki, which was apparently for the
        DIP package of the chip, and got those results. After rewiring for the
        SO version of the chip it works fine.

        Now on to the SD card.


        --- In zipitwireless@yahoogroups.com, "ZipItPet" <aibopet@...> wrote:
        >
        > --- In zipitwireless@yahoogroups.com, "David" <kd7nzk@> wrote:
        > Sounds like a low voltage signal (assuming no wiring errors)
        > It looks like one direction is working (PC->Zipit).
        >
        > The bootstrap program that runs on the ZipitV1 starts with
        > "ZPM .02 - 57.6Kbps new cmds" (see source in ZPM.A)
        >
        > You are getting corrupted data going the other way Zipit->PC
        > (but the fact it is printing anything indicates the PC->Zipit is good)
        > > $b9$$d5$$83$.02 - 57.6Kbps new c$ed$ds$0e$
        > > $0e$$cf$K@>$0e$$0e$$9f$#$e1$cMD ES1$0f$$0b$OK
        >
        > ------
        > IIRC the voltage on the MAX chip should be 3.5V
        >
        > BUT the Max233A chip is officially a 5V chip. If you run it at 3.5V
        > the signals won't be official RS-232 levels, but in my experience it
        > works good enough for most RS-232 ports.
        >
        > BTW: it varies depending on the MAX chip.
        > BTW: each RS-232/COM port has slightly different voltage thresholds
        > on incoming data
        >
        > ------
        > Advice:
        > #1) if you have them available, swap in another MAX-233A chip, cross
        > your fingers and try again
        >
        > #2) if that doesn't work, power the MAX-233A chip with 5V. This will
        > pump up the RS-232 signal levels to official levels.
        > BUT the Zipit RXD signals will be too high (swinging between 0V and
        > ~5V). You should add a level shifter (eg: something as simple as a
        > two resistor voltage divider).
        > NOTE: The Zipit TXD signal will be fine.
        >
        >
        > Good luck
        >
      • Ed Paradis
        Thanks for the heads up!
        Message 3 of 4 , Aug 13, 2008
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          Thanks for the heads up!

          On Wed, Aug 13, 2008 at 2:49 AM, David <kd7nzk@...> wrote:
          > In case anyone else runs into the same problem, it seems the pinout
          > for the MAX233A DIP package and the MAX233 SO package is NOT the same.
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