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Re: [midatlanticretro] EDN article: "The Serial Port: It Just Keeps Going"

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  • Dave McGuire
    ... Discrete components. Transistor-based inverters. -Dave -- Dave McGuire, AK4HZ New Kensington, PA
    Message 1 of 10 , Sep 23, 2013
      On 09/23/2013 03:24 PM, B. Degnan wrote:
      >> I agree! Sales guys at DELL laugh or snicker when I order a computer
      > with a serial port. The card access systems I support at work all use
      > serial port connections. Correct me if I'm wrong, but don't you need to
      > licence USB to use it in your applications? Or am I thinking about SD
      > cards? Why pay more when a simple communication interface that works is
      > free?
      >>
      >> Regarding the inventor of the 1488/1489, try to contact him, it would be
      >> really cool to know more about the origins of these chips.
      >
      > Answer...what did you use before these chips? Relays, right?

      Discrete components. Transistor-based inverters.

      -Dave

      --
      Dave McGuire, AK4HZ
      New Kensington, PA
    • joshbensadon
      ... I have a question about those chips, perhaps you or someone in this group might know the answer. Why did they create them with a NAND function? I mean,
      Message 2 of 10 , Sep 23, 2013
        >> Regarding the inventor of the 1488/1489, try to contact him, it would be
        >> really cool to know more about the origins of these chips.

        >Yes, that's a good idea.

        I have a question about those chips, perhaps you or someone in this group might know the answer.  Why did they create them with a NAND function?  I mean, wouldn't it have been better if these RS-232 drivers/receivers would have been 6 per package instead of 4?  In every design I've ever seen, the two NAND inputs are simply tied together.

        I guess the same could be asked of the 7438.

        J.

      • Dave McGuire
        ... To give them an enable capability. ... This, however, is a different matter. The 7438 is a quad NAND gate with open-collector outputs. There were (or
        Message 3 of 10 , Sep 23, 2013
          On 09/23/2013 06:34 PM, joshbensadon wrote:
          > I have a question about those chips, perhaps you or someone in this
          > group might know the answer. Why did they create them with a NAND
          > function? I mean, wouldn't it have been better if these RS-232
          > drivers/receivers would have been 6 per package instead of 4? In every
          > design I've ever seen, the two NAND inputs are simply tied together.

          To give them an "enable" capability.

          > I guess the same could be asked of the 7438.

          This, however, is a different matter. The 7438 is a quad NAND gate
          with open-collector outputs. There were (or "are", they are current
          products) the 7406 and 7407, which are hex inverters and hex buffers,
          respectively, both also with open-collector outputs. Why people chose
          to use the 7438 in designs instead of the 7406 or 7407 is the question,
          when all they (almost always) did was tie the 7438's inputs together and
          make them like 2/3 of a 7406.

          -Dave

          --
          Dave McGuire, AK4HZ
          New Kensington, PA
        • Neil Cherry
          ... Nand? I always thought of that as enable/disable so you could put into Hi-Z mode. This would allow more than one device on the line though I ve never seen
          Message 4 of 10 , Sep 23, 2013
            On 09/23/2013 06:34 PM, joshbensadon wrote:
            > >> Regarding the inventor of the 1488/1489, try to contact him, it would be
            >
            > >> really cool to know more about the origins of these chips.
            >
            > >Yes, that's a good idea.
            >
            > I have a question about those chips, perhaps you or someone in this group might know the
            > answer. Why did they create them with a NAND function? I mean, wouldn't it have been
            > better if these RS-232 drivers/receivers would have been 6 per package instead of 4? In
            > every design I've ever seen, the two NAND inputs are simply tied together.

            Nand? I always thought of that as enable/disable so you could put into
            Hi-Z mode. This would allow more than one device on the line though I've
            never seen them used that way.

            BTW, I though we just used CMOS before this (triple voltage CMOS as
            I recall: +/- 15v,-5v and gnd). And yes the 88/89 chips were great for
            self sacrifice. I thought that was s design feature (really we used it
            as such). If lightening struck, swap the chips and you were usually good
            to go. Except for that board that came back mostly black ...

            --
            Linux Home Automation Neil Cherry ncherry@...
            http://www.linuxha.com/ Main site
            http://linuxha.blogspot.com/ My HA Blog
            Author of: Linux Smart Homes For Dummies
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