Ok, these things are a little less horrid than they first presented themselves
as. Whenever Lady Heather sends a command to change a setting, it follows it
up with a command to read that setting back from the receiver. It turns out
that the Datum units don't have any (or possible a very small) received message
buffer. Basically they were ignoring any commands sent to them. Increasing
the delay after sending something to the unit got things working better.
You can't stop a survey using the normal Trimble "stop survey" command, but
you can send a fixed position to the unit which will stop the survey. They
definitely don't have an EEPROM for saving settings and location between power
cycles.
Sending the proper Trimble "set broadcast packet mask" message (that tells it
what messages to send automatically) to the unit causes it to stop sending the
primary and/or secondary timing messages. I need to figure out a packet mask
setting that won't hose up both the Datum or any of the Trimble units...
Also it appears that it occasionally repeats or skips a primary timing message
and that causes a "duplicate time stamp" or "missing time stamp" warning if
you send the receiver a "request almanac health (0x29) request. The primary
timing message should be sent exactly once per second and each message should
have sequential and unique time values.
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