>
>How do you figure Motorola is violating the spec? The output of the 1489
>is perfectly well defined for voltages outside the range of -3V ~ + 3V.


Maybe I was speaking loosely.
In the original spec, +3V is a zero, and -3V is a 1
Everything inbetween is undefined.

With mot's receiver, the 0 threshold is a bit less than 3V (ok), but the 1
threshold is near zero, instead of being defininitely negative.  As I see
it, the spec wanted to achieve about a 6V minimum delta, around zero.

A lot of problems in 232 serial stem from people trying to use up all the
margins on their product, and expecting the other guy to be near perfect.

>People that use this characteristic of the 1489 receiver by _driving_ it with
>TTL levels (or outputs that cannot stand being shorted to +/-30V and the rest
>of it) are violating the spec, but Motorola isn't, as I see it.

There's a LOT of outputs out there that can't pass the short to 30V test. :)

Verifone, after Ieft that part of the business, started using op-amps to
drive 232 lines.
Works, but not very robust.
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