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AD7606 FRSTDATA behaving incorrectly, causing problems.

Question asked by bsumlin on May 8, 2018
Latest reply on May 10, 2018 by bsumlin

I'm running an AD7606-6 in parallel interface mode. I have two probably-related problems. The logic analyzer image attached shows that I need to pulse RD seven times to obtain a reading of all six channels, since the first one is always garbage data. This is probably related to FRSTDATA, which isn't behaving as it should according to the datasheet. The datasheet says FRSTDATA goes from tristate to low on the falling edge of CS (or within 18 ns thereof). It then goes high to indicate the availability of the availability of channel 1, and low on the next falling edge of RD, and remains low until all data is read back before returning to tristate.

 

Instead, mine floats high (confirmed by scope readings, too), goes low somewhere after the 2nd falling edge of RD, and returns high on the 7th falling edge of RD.

 

I can get data back reliably by pulsing RD seven times and outright ignoring FRSTDATA, but this obviously isn't robust. What's going on here?

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