[ntp:questions] Oddities in termination of cable from gps18.
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Null at BlackList.Anitech-Systems.invalid
Fri Feb 24 00:09:04 UTC 2012
David Woolley wrote:
> unruh wrote:
>> No, there is the RS232 spec, set up 20-30 years ago,
While RS232-C lasted the longest,
and is likely the most referenced.
RS232 (1962)? ~ 50 years,
RS232-C (1969)? ~ 43 years
RS232-D (1986)? ~ 26 years
>> 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.
That certainly is a good question,
however its hard to maintain compatibility with
things that break the standard they are designed after.
What / where is the TTL compatible non-standard RS232
implementation specification? References?
I've used some current Maxium that switch at ~ 1.5 V;
I've also used some current TI (RS232-F speced),
that don't switch if the voltage remains positive.
> 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).
The current version is TIA/EIA-232-F (1997)
A logic 0 is represented by a driven voltage between 5 V and 15 V
and a logic 1 of between –5 V and –15 V.
At the receiving end, a voltage between 3 V and 15 V represents a 0
and a voltage of between –3 V and –15 V represents a 1.
Voltages between ±3 V are undefined and lie in the transition region.
This effectively gives a 2-V minimum noise margin at the receiver.
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