>> I think that Grey Wolf is right here.  RS232 was defined for TTL
>> voltages.

> RS232 did arrive on the scene at about the same time as TTL, but they
> didn't use the same signal levels.

> "RS-232 was first specified by the EIA in the 1960's" according to
> "RS-232 Simplified" by Byron W. Putman (ISBN 0-13-783499-3, Prentice
> Hall, 1987).  ([This] of course [is] not as authoritative as the
> original standards documents, which I wish I had copies of!  ;-)

I once got a library to dig up a copy of RS-232C.  I don't know about
earlier revs, but the standard I read definitely did not use TTL signal
levels.  I no longer have it at hand, but to the extent that my memory
can be relied upon, this paragraph is right:

> Indeed what it all boils down to is that a logic "1" value is
> represented by a voltage between +3 and +25 VDC, and a logic "0"
> value is represented by a voltage between -3 and -25 VDC.

					der Mouse

			       mouse@rodents.montreal.qc.ca
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