Dale Botkin wrote:
>
>Mabe I'm missing something...  but why would negative-going levels be
>important other than meeting the letter of the RS232 electrical spec?  I
>thought it wuld be a major deal for interoperability, but I have yet to
>see an RS232 receiveer that won't see, say, .4V or below (usually .7 or
>even higher) as a valid LOW signal.  Even the old ones.  Is there a large
>base of devices not using the receiveers I'm looking at (MC148x, MAX2xx,
>etc) or does it make a difference over longer cables?  Noise immunity? I'm
>not disagreeing with your statement, just trying to figure out why to
>agree with it...  8-)
>

Hi Dale,

You are probably correct that <= 0.7v will actually "work" with
most devices - BUT my personal preference is to design to meet
the "minimal" specs, at the very least. Cover the bases. Plain
and simple. And the more recent specs are more stringent than
the older, anyways, +/-5v vs +/-3v.

But Bob Ammerman was the one who was so adamant about using MAX232,
and I was interested in how he felt about +5v/-12v via BJT ckts,
ie, within the actual RS-232 spec range - as against +12/-12v via
MAX232.

- danM

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