Use RTSI and external trigger for high-speed capture

[jmoses]

I noticed Document 2QK7TGLT, which says that RTSI and an external signal can't both be used to trigger the high speed capture lines. 

Does this apply to the motion control boards?

I am successfully using a 735x to do buffered high speed capture of the encoder position, with the aid of an external 2 kHz clock signal.  While this buffer is being captured, I also want to capture a single position, triggered separately, through RTSI.  Is this possible?

Josh

[Jochen]

Josh,

yes, the knowledge base document that you have found refers to NI motion control boards and it is correct. As mentioned in the KB you can't use an external trigger and RTSI for high speed capturing at the same time on a single axis.

Still there are several options to do what you want:

1. If there was an unused axis on your 735x you could connect your encoder signal also to the encoder inputs of the unused axis (e. g. configured as closed loop stepper with following error disabled which means setting a value of "0"). You can use high speed capturing with this axis and RTSI to capture the single position value.
   
   
2. If there is no axis left you could use a counter (e. g. on an M-Series board or a counter board) and configure it for buffered position measurement. You could route the encoder A and B signals through RTSI from the 735x to this board.
   

I hope this helps,

Jochen Klier
National Instruments

[jmoses]

Dear Jochen,

These both sound like great ideas!  Thank you very much!

Josh

[jmoses]

Dear Jochen,

I prefer to go with your idea #1.  I tried it and it is working well for relative positions, but the two axes don't seem to agree on the absolute position.  I need them both to simultaneously reset their position and following error to zero.  Reset Position.flx only does one axis at a time.  I tried wiring two of these functions in parallel, in my VI, but that didn't seem to do the trick.  Can you help with this?

Josh

[Jochen]

As you have found out Reset Position.flx resets only one axis at a time and it doesn't reset the following error. In order to reset both axes these axes need to be stopped (halt stop). After that you should call Reset Position.flx. For more detailed information please follow this link.

Best regards,

Jochen

[jmoses]

OK, thank you!

Josh