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TDC7200: Multi-cycle avg.: Rising START signal flanks seem to be skipped. Calibration?

Frank Perge
Prodigy 40 points
Part Number: TDC7200

Currently I am investigating an issue related to measurement mode 2 with 4 cycles of averaging, expecting two stops per cycle. Looking at the data calculated by the firmware it seems like the TDC7200 skips START signal flanks when the two stop times become bigger (bigger TOF). The data is still intact and my calculations correspond to what I am seeing on my scope. However, the TDC7200 needs more measurement cycles for the same result as before. The interrupt comes later. 

I use a calibration time of 10 cycles was used. I found out, that I do not have problems with START signal skips when I change this calibration time to 2 cycles. How is that possible? Does the second stop trigger a calibration in the multi-cycle averaging configuration?

  • 0
    TI__Mastermind 19630 points

    Hello Frank,

    Thanks for posting to the PS forum! I am trying to understand your test setup here so you are trying to run 4 cycles of averaging with two stop pulses expected per cycle, that makes sense so far. But can you explain what you mean by the START signal flanks as the TOF increases?

    You mentioned skipping the START signal when you are at 10 calibration cycles, are you indicating that the device does not detect the START signal therefore does not start a measurement? The calibration occurs after every measurement and the completion is indicated by a pulse on the TRIGG pin, once that is completed the device is ready for a START signal. Were you checking for a TRIGG output after your measurement before providing a START signal?

    Best,

    Isaac