[ntp:questions] Oddities in termination of cable from gps18.
david at ex.djwhome.demon.invalid
Thu Feb 23 23:12:45 UTC 2012
> No, there is the RS232 spec, set up 20-30 years ago, but since the late
> 80s almost all rs232 receivers have used something like .5V and 1.5V as
> the transitions. In part to ease use of TTL voltages. The more relevant
> question is not whether the rs232 are out of spec, but do you know of
> any rs232 receiver chipsets which do not work with TTL type signals.
The +/- 3volt specification is for the driver. The receiver hysteresis
is smaller and, and at least for control signals the decision point is
supposed to be biased so that open circuit control signals default to
off (the data is also in the opposite logic polarity, so that inputs
default to marking, which was a good thing for mechanical teletypes).
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