PCF8574A: no output work

Tiziano Meneghello

Part Number: PCF8574A

Hi all,

I'm trying to change my older PCF8574AP marked NXP with the PCF8574AN marked Texas Instrument, the problem is that with a working board mounted with the PCF8574AP the Output (2803+relay) works well, if I change with the new device no outputs work. The I2C address is set to be 0x7E. Any idea?

Thanks.

over 5 years ago

0 BOBBY over 5 years ago

TI__Guru 59470 points

Hey Tiziano,

Can you provide a schematic and waveforms of I2C transactions for us to review?

Thanks,
-Bobby

0 Tiziano Meneghello over 5 years ago in reply to BOBBY

Prodigy 60 points

This board is older more than 10 years but I've used only the NXP product so I think that is not a problem on I2Cbus because is made very simple SDA/SCL; A0/A1/A2 is pull-up; P0-P7 is connected direct to ULN2803A; INT is not connected. For the schematic I have to search on the archives..

0 Miguel Robertson over 5 years ago in reply to Tiziano Meneghello

TI__Guru 62920 points

I agree with Bobby that seeing the I2C waveforms and schematic would be helpful, since generally we would expect equivalent functionality between these two devices. Beyond that, do you know if you are able to read from the device properly? Or, do you know if the device is responding to I2C transactions with an acknowledgement (ACK) bit?

Regards,
Max

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PCF8574A: no output work