[time-nuts] X72 and 1pps

Stephan Flor spflor at yahoo.com
Sun Mar 4 23:10:04 EST 2018


Matthias,
I'm working on the same project. It looks like you should only be able to get the difference between the two 1pps signals out of the rs-232 port. Maybe Heather can display it?

This is from the X72 designers reference manual
"A 1 PPS output is an integral part of the design.An optional 1 PPS input allows the unit to track aGPS or other external reference, and display thedifference between the input and the 1 PPS generatedby the X72 through the RS232 link."
"3.4.2 X72 1 PPS Input and OutputThe 1 PPS output signal of the X72 unit is positive edge triggered and gated with the rising edge ofthe clock. It’s duration for a 10 MHz unit is 400 ns ±10%. Rise/fall time is 4 ns.The 1 PPS is exactly divided from the XO frequency.Future implementation will support tracking, synching and smoothing of incoming 1 PPS toproduce the output 1 PPS."
Stephan




 

    On Sunday, March 4, 2018 6:47 AM, Matthias Jelen <Matthias.Jelen at gmx.de> wrote:
 

 Hi Mark,

thanks for your reply.
> Try enabling the PPS input form the "P menu.
I can´t find this option - I can toggle the PPS output, but 
not the input.

BTW, what´s the "set TIC" option? I can enter a number here, 
but I can´t find something about this command in the manual...

&a Auto-Tune seems to work well - I see the plot stepping 
and a slope is calculated.

What´s the expected behaviour if I go to d-e: "Enable HW 
discipline" ? I can´t see any changes here.

I checked the SA.22.C manual as well, but this contains more 
or less the same information as the X72.

Regards,

Matthias
> Also, to verify that it is using the PPS input try the &a auto-tune command.  It will set the TIC  and DDS tune word to to 0, collect data for for however long you requested (an hour is a good start), then calculate the drift rate and set the DDS tune word to put the device on frequency.  The EE command should set save the DDS word in EEPROM.    If the unit is seeing the PPS input, you should see the PPS plot stepping as the DDS freq drifts.
>
> Many of the X72 settings cannot be read back from the unit.  Heather maintains a "software eeprom" with the settings that it knows about in the file "tbeeprom.dat".  Until you update a setting, what is displayed for that setting may not be correct.  Use the "P" menu to set each of the settings so that Heather can learn what they are.  When Heather starts up, it restores all the last settings from the file.
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