I have gotten PPS/PPSAPI from my Novatel working somewhat, but I am
using nist.time.gov as my reference. Now to configure the system to
use my GPS for the timestamp.  I have a few questions regarding this:
1) since DCD is probably not being used for communicating with the
Novatel, can I use a single cable for optaining the PPS and the
messages from the receiver
2) what message format does the PPS need
3) will my interaction with the Novatel affect the PPS api's ablity to
obtain the needed messages?

btw, I REALLY appreciate this group and hope that I can contribute as
my knowledge of NTP grows.

kind regards
chris

Hallo Chris,

I don't know the Novatel, but a few general comments may help.

1) Typically, you just need 4 wires: RXD, TXD, DCD and GND.
   No problem for a typical 9-pin or 25-pin serial port.

2) The 'message format' of the PPS signal is very low-level :-)
   It's just a voltage level that changes once per second,
   i.e. a rectangular pulse-train. The high and low voltage levels
   are often either TTL or RS-232. You'll have to check the specs
   for the GPS and the computer, and you may need a level converter.

3) It depends... If your interaction includes disabling the PPS output
   from the GPS, then the answer is 'yes'! In general, it's best to use
   the GPS as part of a dedicated NTP system and not interact with it.
   Just reading the messages from the GPS on a second computer is no
   problem -- you might want to do this for statistical evaluation,
   to check satellite health or whatever.

Hope this helps,
Paul

chrish@navsys.com (clh) wrote in message news:<9a6d1f4c.0402191304.a36b040@posting.google.com>...
> I have gotten PPS/PPSAPI from my Novatel working somewhat, but I am
> using nist.time.gov as my reference. Now to configure the system to
> use my GPS for the timestamp.  I have a few questions regarding this:
> 1) since DCD is probably not being used for communicating with the
> Novatel, can I use a single cable for optaining the PPS and the
> messages from the receiver
> 2) what message format does the PPS need
> 3) will my interaction with the Novatel affect the PPS api's ablity to
> obtain the needed messages?
> 
> btw, I REALLY appreciate this group and hope that I can contribute as
> my knowledge of NTP grows.
> 
> kind regards
> chris

>2) The 'message format' of the PPS signal is very low-level :-)
>   It's just a voltage level that changes once per second,
>   i.e. a rectangular pulse-train. The high and low voltage levels
>   are often either TTL or RS-232. You'll have to check the specs
>   for the GPS and the computer, and you may need a level converter.

Most RS-232 receivers work fine with TTL (or 5V CMOS) signals.

For a one-off setup, I suggest trying it before going through
the effort/expense of setting up a converter.  If you are going to
be setting up many systems, it might be worth the effort to find
a clean setup that meets all the specs just so you don't have to
worry about the finger pointing when something doesn't work.

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