Original question:
Part Number: TCA6408A
Hi there:
I'm helping customer to check an question about non-acknowledge with TCA6408A
the following is the relative information we've collected
1. we've try to modify the pullup resistor into 10K ohm, still no response
2. Do we have other suggestion for customer?
schematic
&
comment snapshot
waveform measured
Hey Kay,
I believe the problem is that you are addressing our device and then sending a read bit.
From the bit analysis I see:
1) 0x010 0000 (our address)
2) bit 8 is 1 meaning a read
3) last bit is a 1 meaning an NACK
Our I/O expander actually will NACK if you sent a read bit without doing a write previously. Please refer to this diagram in the datasheet:
Notice inorder to do a proper read, you must:
1) send the device address with a write bit
2) send the address you want to read from (think of this as adjusting a pointer in a software sense)
3) either initiate a stop condition then a start condition or if you have multiple masters on the bus, initiate a repeat start
4) send the device address again but this time send a read bit instead
5) from this point on the IO expander will become the transmitter (on data line, master still needs to send clock pulses)
6) master should ACK to receive more bytes or NACK to stop receiving bytes
I believe if you want to verify this device works, you should just send a write bit after the address to receive your ACK.
Thanks,
-Bobby
