PCF8574ADGVR address issue

Thomas Lam86

Other Parts Discussed in Thread: PCF8574, PCF8574A

I have issue with addressing of the PCF8574DGVR. According to the specsheet of PCF8574 on page 13 if A2(Pin 9)=L and A1(Pin7)=A0(Pin 6)=H, the internal address of PCF8574 is 71 for read and 70 for Write. I have a test board and read it with a bus pirate and I search for address for the PCF8574; I read back address 76 for write and 77 for read. I tried this on two PCF8574 ICs and both the same. Please advise. Thanks in advance for your help.

Direct read from BUS interface:
I2C>(1)
Searching I2C address space. Found devices at:
0x76(0x3B W) 0x77(0x3B R)

over 7 years ago

0 Siby James over 7 years ago

TI__Expert 5140 points

Hi Thomas,

I've looped in the appropriate contact for this question.

Thanks,
Siby

0 Michael J Schultis over 7 years ago in reply to Siby James

TI__Mastermind 24485 points

Hello Thomas,

I believe I know what your issue is. Please note that the PCF8574 and the PCF8574A are distinct devices.

I believe you may have the PCF8574A device and you are looking at the datasheet for PF8574. These devices are the same but have slightly different addressing internally.

If you look at the address reference for the PCF8574A then you get 0x77 for Read and 0x76 for write, while the PCF8574 is 0x71 for read and 0x70 for write.

Does this make sense?

Best,
Michael

0 Thomas Lam86 over 7 years ago in reply to Michael J Schultis

Prodigy 20 points

Thank Michael, I looked up PCF8574A spec sheet after I posted the question on Friday and realized the PCF8574 and PCF8574A have totally different internal address so yes thanks!

Our CM in Asia actually using PCF8574T? Do you know this IC exist? Or it's a part of either PCF8574 or PCF8574A? Thanks again.

Thomas

0 Michael J Schultis over 7 years ago in reply to Thomas Lam86

TI__Mastermind 24485 points

Hello Thomas,

Happy to help. To be honest it looks like the PCF8574T is not a TI device.

Best,
Michael

Interface

Interface forum

PCF8574ADGVR address issue