[ntp:questions] Oddities in termination of cable from gps18.

David Woolley david at ex.djwhome.demon.invalid
Thu Feb 23 23:12:45 UTC 2012

unruh wrote:

> 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).

More information about the questions mailing list