UCD9081EVM: NACK on I2C read command

Nicholas Carley

Part Number: UCD9081EVM
Other Parts Discussed in Thread: UCD9081

Hello,

My customer is using the UCD9081EVM and trying to communicate with it using a general USB-I2C device.

They have J17-J20 (ADDRx pins) all set high so the address is 0x6F. They did power cycle after setting the ADDR pins to make sure their took effect.

but, their read command is coming back as NACK, scope shot below.

Any thoughts on things to test or debug next? Are there any other I2C settings we overlooked?

Thanks,
Nick

0 yihe over 2 years ago

The waveform does not follow the protocol.

Also make sure the speed is less than 100KHz.

Regards

Yihe

0 Nicholas Carley over 2 years ago in reply to yihe

Hi Yihe,

yihe said:
Also make sure the speed is less than 100KHz.

Is it less than 100kHz or less than 400kHz?

For the waveform, I'm not sure what I'm missing.

+1 yihe over 2 years ago in reply to Nicholas Carley

Thank you for pointing out. it was a typo and I had fixed it. UCD9081 supports up to 100KHz.

The waveform does not follow the protocol:

for read: Start bit + (address + W) + REG_ADDR + RS(Repeated START) + (Address +R)

Application can not jut send out Start Bit + (Address + R) + REG_ADDR.

The read must start with Write at the beginning.

Regards

Yihe

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