[time-nuts] TruePosition GPS Receiver

ziggy9+time-nuts at pumpkinbrook.com ziggy9+time-nuts at pumpkinbrook.com
Sat May 6 21:13:08 EDT 2017

I picked up two of the parent units (the LMU300 19” rack mount chassis) and have also managed to find a copy of the installation document manual (for deployment and installation of the hardware, and system turn up procedures).  It is of limited use since there is very little you can do with the GPS(DO) module besides setting the location and checking satellites. But if you have the chassis and want to play with it contact me off list.

A couple of observations on the LMU300:
- the console port is the AEP port, a 6 pin RJ-11 - and you need a 6 pin connector
- the USB port is non-functional
- pin 1 (furthest left looking into the jack) is ground, pin 1 (furthest right) is LMU300 txd, pin 3 is LMU300 rxd 
- 115200,N,8,1 speed and format
- the unit *will not boot completely* on it’s own due to missing T1/E1 signaling from the SMLC
- the unit *will not boot completely* without GPS initialization
- both of the above conditions can be bypassed :)
- in spite of the above, both of my units are still unhappy and eventually reboot with watchdog timeouts or other errors

A few notes on the GPSDO module:
- the 5 pin header near U19, the LM74 temp sensor:
    - pin 5 or the third pin in the row closest to U19 is the 12v input (measured). the other 4 are all ground.

- the 15 pin header:
    - pins 1,2,5,6,9,10,13,14 are all ground
    - pins 3 and 4 are 3.3v ttl level, I’m guessing another serial port
    - pins 7 and 8 are 3.3v ttl level, and contain the same data as J2 pin 2
    - pins 11,12 are 1 pps, 10ms, 5v

- the 6 pin header, J2:
    - pin 1,4 are ground
    - pin 2 is output from the module, pin 3 is input?
    - pin 5 may be hardware handshake (like CTS/DSR/DCD)
    - pin 6 looks like the Furuno data - lots of $PFEC strings

- the unused MCX connector is 1pps, 10ms, 5v buffered by 74AC74

- software wise, what I see so far is similar to the Packrat info. $CLOCK, $STATUS messages etc. I did note an $EXTSTATUS message, but that’s the only new thing so far. If i discover anything useful/interesting I’ll send an update.

The GPS engine is a Furuno GT-8031, not sure why it hasn’t been findable but the manual is on KO4BB’s site:
<http://www.ko4bb.com/manuals/ <http://www.ko4bb.com/manuals/>>

The OCXO on my unit is a CTS 196 series. It’s advertised as ‘low phase noise’. Datasheeet here:
<http://www.xtal.cc/UploadFiles/Product/20161101163222_40783.pdf <http://www.xtal.cc/UploadFiles/Product/20161101163222_40783.pdf>>

Again, contact me off list and I’ll send the LMU300 doc or a pointer to it.

Paul - K9MR

> On May 5, 2017, at 11:30 PM, Mark Sims <holrum at hotmail.com> wrote:
> I got in my Trueposition GPSDO's today and have one running.   These units are a little bit different than the Packrat documentation.  There is no second serial connector.   The first three pins on the 6 pin connector are RS-232 at 9600,8,N,1   You need to jumper pins 4 and 5 to talk to the board.
> The power connector is different.  It is a 5 pin connector on the back of the board.  4 pins are ground and VCC is the other pin.   Check with an ohm meter to make sure you connect up properly...  the GND/GND/15V in the Packrat doc is backwards!   Mine is running just fine on +12V... YMMV.
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