external Clocksource for MCC172

[Martin Wollatz]

I would like to use an MCC172 with an accurate time base. An atomic clock (CSAC) is built into our devices, and I can divide the PLL out as desired. Is it correct that the GPIO19 can be used for this? At least there is a rectangle with 5.24MHz when I configure the MCC172 with SOURCE_MASTER.

[JRys]

The MCC 172 is not designed to use an external clock because the clock runs 512x the sample rate, and a sync pulse is used to synchronize the ADCs. GPIO 19 is used to clock other MCC 172 boards on the RPI stack, and a sync pulse on GPIO 6 synchronizes all the ADCs. None of the other MCC daqhat boards can use its clock. After the sync pulse is set low, it takes 128 conversions before data is ready.  You can make the clock appear on GPIO 19 using the SOURCE_MASTER clock mode with the mcc172_a_in_clock_config_write function. 

 

[Martin Wollatz]

Thank You for the fast reply.

I wanted to switch off the on-board clock on my MCC172 with SOURCE_SLAVE. I am familiar with the connection between clock and sampling rate in a delta sigma converter.