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RS232 Voltage Levels

Discussion in 'General Electronics' started by Charles Jean, Jan 5, 2006.

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  1. Jim Thompson

    Jim Thompson Guest

    360mW typical ;-)
    Keep in mind this was early '60's.

    Quite a few process capability improvements since then.

    ...Jim Thompson
  2. Roy L. Fuchs

    Roy L. Fuchs Guest

    Sounds like a poorly implemented utilization. Sum Ting Wong must
    have done the design.
  3. Roy L. Fuchs

    Roy L. Fuchs Guest

    PS: I refer to the circuit designer, not the chip.
  4. Connected and driving, it sure seemed like more! But I think the
    RthetaJA was about 150. Which meant 'damned hot' even at .36W.

    With as little as 4k or so on the 1489 receiver inputs, that was
    getting near another tenth watt dissipation per connected input at
    that end, with +/-12-15V signaling applied, too. Part of the spec,
    sure; but still ...

    There was an advantage to all this, I suppose. I could find the 1488
    and 1489 parts blindfolded. Just casually feel where the heat is
    emanating from. ;)
    No doubt. I didn't get around to using them until much later, though,
    being that I was in grade school in the early '60s.

  5. Charles Jean

    Charles Jean Guest


    I'm the OP of this thread and would like to thank everyone for such a
    voluminous and knowledeable response! For those that wanted to know,
    the chip is the SV2000 video interface chip from It inputs serial ASCII data and converts
    to an RS170 composite video encoded stream. It is supposed to give a
    9 line X 16 character display, with a standard ASCII font as well as
    user-defined fonts. Control commands are preceeded by ASCII 27(ESC).
    It has been marked down from $20 from $10. I already had a portable
    BW TV with a composite video input, so I thought I might try it. By
    bit-banging I wouldn't use the precious single UART of my uC, and only
    one of its output pins.

    As you can see from the data sheet, the connection on pin 6 allows for
    either "normal" or "inverted" TTL levels to be used. I think I could
    have saved lots of confusion by rephrasing my question to: "What's the
    idling voltage of normal and inverted TTL serial lines?" I can write
    the program to have the line at pin 3 idle at either 0 or 5 volts, and
    I had a 50-50 chance of having pin 6 wired correctly. Just lazy
    again. Sorry if I caused any trouble.

  6. Yeah, they don't know what they missed by never working on the old AP
    & UPI newswire KSR33 teletypes on a leased loop.

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
  7. Don Bowey

    Don Bowey Guest

    Or the models 14, 15 and 19 that were even before your time. They seemed
    hi-tech at the time. My first one at home was a 14 with the range crank on
    top, front. It came from a Telco Toll office.
  8. Roy L. Fuchs

    Roy L. Fuchs Guest

    Well... take a bow.
  9. Mark Zenier

    Mark Zenier Guest

    33's were uppercase ASCII. I think the wire services used 5 bit machines.
    The ones with the type box were 28s. I think the 5 bit code corncob
    machine was the 32.

    Mark Zenier
    Googleproofaddress(account:mzenier provider:eskimo domain:com)

  10. I had a model 15 of my own, (Found at a Dayton hamfest) but I used
    the KSR33 a lot more. We had two of them at the military radio & TV
    station I worked at in '73 & '74. They replaced our very worn out
    Kleinschmidts. :) Later on I had a Metrodata computer with two 20 mA
    boards for AP & UPI news wires at a United Video Cablevision CATV
    headend in Cincinatti, Ohio. I was troubleshooting one of the six
    channel Metrodata graphics computers when I found a couple undocumented
    commands. One that let me interrupt the 20 mA loop. The other let me
    type and send messages on a "Read only" system. It wasn't long after
    that that the hardwire 20 mA loops were replaced with receive only sat

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
  11. Chuck Harris

    Chuck Harris Guest

    The wire services used 5 bit machines, such as the model 15, 19, and 28.
    The model 15 is what all of us old fogies remember as the intro to US nightly
    TV news. They always started and ended with a few seconds of model 15
    teletype chatter... Walter Cronkite would fill in the time in between.

    The model 32 was a baudot (5 bit) version of the model 33 ascii machine.
    It was designed for extremely light duty use, such as a small business
    would need for Telex duty. For those that don't know, or remember, Telex
    was to business in the 1970's what the fax machine was to business in the
  12. We would have been better off with 28:30 of TTY SFX. :)

    I just heard a radio spot the other day with TTY SFX in the
    background and the announcer using his best "radio announcer"
    voice (a parody on news-flash style). It was interesting that the
    sound of the old TTYs is so anacronistic these days.

    I was a college freshman running the college radio station
    solo when they made the mistake and sent the REAL missle
    attack message over the wire (instead of the regular sunday-
    morning test tape). That gave us a morning of excitement.

  13. There are two stories I remember coming across the news wire while I
    was at work in broadcast stations. the first was about a tower collapse
    at a station that killed most of the tower crew, and just missed the
    engineer who dived under one of the old RCA broadcast consoles as the
    tower came through the roof and landed on the console. The other was
    the murders of "String Bean" (and his wife Ramona) who was a comic on
    WSM's "Grand Ole Opry". they were robbed and murdered in their front
    yard because he was known to carry a lot of cash on him, due to his
    mistrust of banks.

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
  14. Rich Grise

    Rich Grise Guest

    Some guy once gave me what I'm almost sure was a "model 13". It used a 60
    mA current loop, and ran at "60 WPM" - that's words per minute, where a
    "word" is five characters. So, five characters per second, and five bits
    per character, with start and stop bits, that's not very many baud. Back
    when I was a young stud with an 8008 and .256 KB of RAM, it wasn't that
    hard to make it type stuff. ;-)

    Mechanically, it was fascinating. And if you ever get one, don't spray it
    with WD-40. On a mechanism like a teletype, WD-40 turns to glue. I spent
    about two weeks with a typewriter brush and isopropyl alcohol cleaning
    the damn thing up.

    But it was kewl, toggling stuff into the ol' Scelbi 8H and having the ol'
    model 13 kachunk it out. :)

  15. Rich Grise

    Rich Grise Guest

    Oh, no trouble at all! We like getting into these lively discussions
    and thread-drift. ;-P

    Anyway, all I was going to say is try it both ways, especially since
    you can do it in the micro. Send it some A's and 5's with '0' idle,
    and see what shows up, and send it some A's and 5's with '1' idle,
    and see what shows up. At least that's how I'd do it. "RS-232" has
    always done that to me. :)

    Good Luck!
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