Re: RS232 Voltage Levels

Jan 06, 2006 4 Replies
B


On Fri, 06 Jan 2006 18:36:03 GMT, Jonathan Kirwan


> Gave us:
>
>>>>
>>>>>>
>>>[snip]
>>>
>>>> There may still be some devices that will convert RS-232 levels to
>>>>TTL and some that go the other way.
>>>
>>>RS-232 -> TTL = MC1489
>>>
>>>TTL -> RS-232 = MC1488
>>>
>>>These chips are still available more than 40 years after I designed
>>>them ;-)
>>>
>>>These chips adhere to the original RS-232 spec.
>>>
>>
>>1488 requiring several supplies -- and runs hot as a pistol, too. I've
>>got a box of both; they were about all there was to use in the market
>>and worked well when I was using them; but don't use them much now
>>because of the power requirements (especially the 1488) and the
>>serious heat to be removed (again the 1488 much more than the 1489, if
>>memory serves, but neither of them slouches in the heating
>>department.)
>>
>
> Sounds like a poorly implemented utilization. Sum Ting Wong must
> have done the design.

They always worked well for me - and everyone else in the industry for about 20 years...


Bob



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B

The RS-232 specification was originally designed as an interface for electro-mechanical printers, using discrete transistor logic to convert signals coming over telephone pair hooked up to the old relay-switched public telephone system into successive ASCII characters printed on a rol of paper.

Search on "Telex" and "TWX". It up-graded the original 50/75 character-per-second telex system whose only active components were electro-mechanical - essentially relay logic.

You should be able to find a history of the ASR-33 terminal somewhere on the web - that was the cheap version of the ASR-35 bought by people who had to handle significant amounts of TWX traffic.

Bill Sloman, Nijmegen
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J

What is "Fuchs"? Shorthand for f*ck-head? I plonked him weeks ago. I recommend everyone else do the same.

...Jim Thompson

| James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | | http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
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U

German word for "FOX"

-- Uwe Bonnes snipped-for-privacy@elektron.ikp.physik.tu-darmstadt.de

Institut fuer Kernphysik Schlossgartenstrasse 9 64289 Darmstadt

--------- Tel. 06151 162516 -------- Fax. 06151 164321 ----------

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B

Nope. The ASR-33 was 20 mA current loop - not RS232.

Bob

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