[time-nuts] X72 and 1pps

[Mark Sims]

>  I can´t find this option - I can toggle the PPS output, but not the input.
OK, I remember now...  the X72/SA22 with firmware disciplining have a bit in 
the control reg that reports if a PPS input has been seen.   I found some 
obscure reference that implied you could disable the PPS input, but that did 
not work, so I removed that option.


>  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...

The SET TIC command issues the X72 "k" command to set the TIC offset register.  
 It is used to null out offsets in the value of the TIC register.  Note that 
this command takes 6 seconds to complete.


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

First, you need to have the PPS output enabled for disciplining to work.  Then 
you have to pray to the Gods of X72 Crapitude that the hardware disciplining 
works.  You need a good PPS input.  It can take a long time (or forever) for 
the X72 to decide the PPS is good enough to use.  I have had a lot of issues 
getting the firmware discipling to work.   
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Re: [time-nuts] X72 and 1pps

[Stephan Flor via time-nuts]

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  
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...

 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  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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Re: [time-nuts] X72 and 1pps

[Matthias Jelen]

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...


 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  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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[time-nuts] X72 and 1pps

[Mark Sims]

Try enabling the PPS input form the "P menu.

Also, to verify that it is using the PPS input try the  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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[time-nuts] X72 and 1pps

[Matthias Jelen]

Hello Time-Nuts,

thanks to Mark´s breakout board I was able to fire up my X72 
rubidium. It seems to work fine.


FW is 5.19.

As far as I understand from the (rather crappy) manual, I 
should be able to discipline it to 1pps, but I wasn´t lucky 
using the commands from the manual.


I switched to Lady Heather. It looks like I get TIC results 
from the X72 - The mode is reported as "Free running", so I 
guess this is the difference between the incoming PPS and 
the local one. So far so good, but if I try to enable HW 
disciplining, nothing happens. Also strange, "PPS IN" is 
reported as "OFF"...


Did anyone on this list sucessfully discipline the X72 to 
external PPS? Or has a manual that fits better to the 5.19 
FW? Or can shine some light on how the X72 1PPS feature is 
supposed to work? Any hints are highly appreciated.


Thanks & regards,

Matthias
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