I have to admit I have no real interest in the immediate GPS output of the Furuno, because better engineers than me have sorted that stuff out into the Symmetricom GPSDO with a FFOM of at least 2.
I would like to know what the TOD data packets are, like when you enable TOD EN on SER2. There is also the SER1 output which I haven't probed yet but is most likely the TOD output in binary from what others have stated.
An interesting serial request is PTIME:TCODE? - this is not listed when you issue the ? help command, but is in other Symmetricom documentation.
T1xxxxxxxxtlfrvcc
xxxxxxxx is the date and time of the next 1PPS pulse, referenced to GPS time as number of seconds since 1980/01/06 00:00:00
There can sometimes be a little delay when you issue this command, no doubt to make sure it doesn't respond too early as it is the predicted time of the next 1PPS pulse.
ETA: My ebay bidding sniper wars require such accuracy
But seriously, I suspect all the banksters "high frequency trading" must rely on this stuff.