SPI MISO pin driven by both optical isolators concurrently

[nkrackow]

The SPI MISO pin on the "normal" ground side is actively driven low/high by both HCPL-092J optical isolators at the same time. I see good signals (>4.5 V high) on the isolated side coming from the DAC but only about 0.5 V high signal level on the "normal" GND side. Signals going to the DAC look good too and it's obviously trying to answer. I'm pretty sure this is because the other isolator chip tries to keep this node low since its isolated side is low because the other DAC isn't selected and therefore it's MISO is low. I can also see significant ripple with similar frequency content to the SPI traffic on the isolator chip power, which could mean that it's pumping a lot of current.

[bbradzik]

Suggested temporary solution: lift pin 6 of the IC10B.