[ntp:questions] Very large jitter and offsets on GPS ref clock after upgrade to "p5"

Chuck Swiger cswiger at mac.com
Tue Jan 10 15:43:13 UTC 2012


On Jan 9, 2012, at 11:25 PM, David J Taylor wrote:
>> Searching for "RS232 over RJ45" suggests the standard pinout is known as EIA/TIA 561.
>> Basically, it closely resembles the EIA/TIA 574 (DB9) wiring, but DSR and RI have been combined.
> 
> I was expecting that, for timing purposes, the four pairs would be used as:
> 
> - TXD/ground
> - RXD/ground
> - DCD/ground
> - unused
> 
> i.e. that every relevant RS-232 line was carried with a ground on the twisted pair.  This would be better than some random "pushing of pins"!

It sounds like you are actually looking for balanced/differential wiring, which would be RS-422 (as the other David mentioned).  This would have much better timing characteristics and common-mode noise rejection, and thus permit operation at much higher speeds over longer distances.  You'd need a RS-422 to RS-232 converter with most commodity PC serial ports, as they tend to use a descendant of the NatSemi 8250/16550 UART, instead of something like the Zilog UARTs used by some multiport serial/PBX cards.

Regards,
-- 
-Chuck



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