At 10:57 PM 2/1/2011, Chris Albertson wrote...
I could have a "plumbing" pproblem as the UT+ is 3rd floor and the computer is 1st floor with 75 feet of RS232 over cat-5 between.
Has the PPS been converted to RS232, or are you simply using the TTL level PPS signal?
The docs say it's a "5V" signal, but I suspect it's actually 5V TTL levels. TTL (74LS00 specs here) high level is only guaranteed to a minimum of 2.7V (3.4 V typical), with pretty low output current (0.4 mA). Signals below 3 V are undefined in RS232, and receivers must provide a termination resistance of no greater than 7K Ohms, which is a pretty hefty load for TTL. TTL into an RS232 port usually works, although it's pretty obviously NOT guaranteed to, by spec.
If the signal is indeed TTL, simply adding a pullup resistor to the PPS signal may help. TTL can sink much more current than it can source, so something like a 2K pullup to +5V would be about right.
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