PCI-6115 RTSI 20MHZ timebase input

[src42]

What are the signal requirements for inputting a 20MHz timebase to RTSI pin7 on the PCI-6115 board? The signal will be generated by a non-NIDAQ source.

[Eric_L]

Hello,

The RTSI lines should be running with TTL logic.

Here is a document listing pinouts for the RTSI cable if you need a reference.

https://www.ni.com/en/support/documentation/supplemental/18/rtsi-connector-signal-mapping-and-pinout...

I want to know a little more about your application so I can provide the best solution/ suggestion possible. Will you be using this 20MHz timebase for a counter task on the 6115 or some different analog/digital task?

Eric

[src42]

The PCI-6115 is performing multiple counter output, analog output, and signal A/D tasks. The 20MHz RTSI signal functions as a master timebase input. I am forced to frequency-lock the 6115 with another (non NI) instrument that only has an available 10MHz timebase, which we do by frequency doubling the 10MHz. This works, but I am investigating alternate ways of doubling the 10MHz timebase. 

[Eric_L]

Hello,

You best method may be to input the 20MHz signal over the RTSI line as you are planning. At the moment, I do not have any other suggestion for phase locking the card with a non NI card.

Eric

[src42]

There are various external means of generating a 20MHz master time base signal for the PCI-6115 from our somewhat asymmetric 10MHz rectangular wave. Some of these techniques, based on digital circuitry, can create a signal with a dominant 20MHz component, but residual harmonics at multiples of 10MHz. In the time domain, this means that adjacent rising edges may not have equal 50ns separations, even though alternate edge pairs are separated by 100ns. For example, if the edge times are 0ns, 50.5ns, 100ns, 150.5ns, 200ns ... is this an acceptable 20MHz master time base for the PCI-6115?

[John_P1]

Hi src42,

You could use your 10 MHz signal instead--20 MHz is just the maximum (see S Series User Manual) for the Master Timebase.

Subsystems (AI, AO, Counters, etc.) can also specify their own external timebase.  By default the Master Timebase is used, but if you'd like you can specify your 10 MHz to be used for the subsystem timebase instead of the master timebase (e.g. for AI you would use the AI Sample Clock Timebase).

Best Regards,

[Eric_L]

Hello src42,

What John said is correct. The use of the 10MHz clock can be used to run the 6115. At the time, it did not dawn on me that you may not need a 20MHz time base to run your task (Unless you need a synchronized 20MHz signal for your counter tasks also). Also, the asymmetry of the 10MHz clock should not cause an issue if you are using it directly for your 10MHz time base. John, would you be able to confirm this?

Eric

[John_P1]

Yeah the duty cycle is flexible as long as you meet the minimum pulse width specifications.

Best Regards,