Question
I can't change channels on the AD7998, I get the same value 8 times. Can you
give a recommended sequence to change channels over I2C?
Answer
START
Write Address
ACK by AD7993
Command mode byte 0x30 (set command bits to 0011 and address pointer bits to
0000) On the 5th SCL rising edge of the command/pointer byte the ADC will power
up and convert on ch1
ADC ACK
Repeated Start (ensure this is not a stop condition)
Read address (part power up and converts on ch2)
ACK by AD7993
MSB byte of conversion result ch1
ACK by master
LSB byte of conversion result ch1
ACK by master (part powers up and converts on ch1 again)
MSB byte of conversion result ch2
ACK by master
LSB byte of conversion result ch2
NACK by master
STOP
Once the command bits are set in the command/address pointer byte the ADC
starts to operate in mode 2. When ever the part receives a STOP or NACK
condition it will no longer operate in mode 2 until the command bits are again
programmed to do so.