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So it seems like the device is waking up. More debugging to do. Liam Hawkins any ideas?
The AFE takes time for the references to wake up, and it takes about 3.5mS for the AFE to wake up the references. It shows 5mS here, but would be within the specified range if measured from the end of the rising edge.
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Reading further, this wait cycle only applies when waking up the AFE to measure it.
So we went on testing trying to get data from it.
We connected a logic analyzer to the output to see if we were getting the correct data out. The output shows the same data that we send in code, so this verifies that we have the correct SPI port and pinouts. However, still no response from the AFEs.
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We looked at the ISOSPI input on the AFEs with an oscilloscope, and that all seemed fine:
Note - the peak are much higher (>+-1V) when zoomed in.
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So the data is getting to the AFE side accurately. It is waking up from the communication and powering the DRIVE pin to enable the 5V regulator - the green LED on the board turns on - and then goes back to sleep after 2s.
We did notice that the MISO and MOSI lines seem to be following each other, which I didn’t really expect. The MISO/MOSI pins seem to be shorted on the board, but I remember Liam Hawkins mentioned at one point that the LTC6820 chips are not ‘idle’ - they will actively drive some of the lines and might be causing this measurement?. We should probably do some more digging into the LTC6820 datasheet to see what we should expect on the SPI port.
Any thoughts Liam Hawkins ?