Steps to communicate to PCF8574 IO expander

Muthu Shankar

Other Parts Discussed in Thread: PCF8574

Hello,

I am using three PCF8574 IO expander as slaves and PIC18F4620 as Master. In My application, I have to switch ON relays connected at 8 port pins in a IO expander So, in My case, I am going to use all port pins in IO expander as output (write mode only). For that, Should I send any command bytes to configure port pin direction? and What data should I send to switch on relays connected after master addressing slave. I didn't get that configuration details from datasheet. Below is the schematic that I have used in My application. Please suggest a solution.

over 7 years ago

0 Joachim Wuerker over 7 years ago

TI__Mastermind 20845 points

Hi Shankar,

welcome to our forum.
Are you certain the PCF8754 is a device from TI?

I am moving your post to the I2C forum.

Regards,

0 Muthu Shankar over 7 years ago in reply to Joachim Wuerker

Prodigy 235 points

Hi Joachim Würker,
Thanks. Yes, it is the part from TI. Below is the My PCF8574 IO expander digikey part link
www.digikey.com/.../484579

Thanks,
Shankar

0 Joachim Wuerker over 7 years ago in reply to Muthu Shankar

TI__Mastermind 20845 points

Hi Shankar,

alright. Now I see it. There was a typo in the part number. I updated the thread title and your post above to show the correct part number.
I will let my colleagues from the I2C forum answer your question.

Regards,

0 Muthu Shankar over 7 years ago in reply to Joachim Wuerker

Prodigy 235 points

Hi Joachim Wurker,

I tried with PCF8574P from NXP. This is working fine with My I2C code. Please tell me what is the difference between Your part and NXP part. I compared those two parts datasheet. I don't see any difference between two parts. I think that I received the faulty parts from Distributor. Please let me know where is mistake.

Thanks,

Muthu

0 Joachim Wuerker over 7 years ago in reply to Muthu Shankar

TI__Mastermind 20845 points

Hi Muthu,

I am sorry, but I am not an expert on those I2C IO expanders.
One of my colleagues from the Interface team will have to comment on your question.

Regards,

0 Muthu Shankar over 7 years ago in reply to Joachim Wuerker

Prodigy 235 points

Hi Joachim Würker,
Thanks. Please take him to answer this as soon as possible. Because, we have to purchase new part if part is faulty.

Thanks,
Muthu

0 Muthu Shankar over 7 years ago in reply to Joachim Wuerker

Prodigy 235 points

Hi Joachim Wurker,

PCF8574 from NXP is working but the same part from TI is not working for me.Coming to Spec, both are same. I am still waiting for your reply. Please respond me.

Thanks,

Muthu

0 Joachim Wuerker over 7 years ago in reply to Muthu Shankar

TI__Mastermind 20845 points

Hi Muthu,

as mentioned before, I am unfortunately no expert on those devices.
I notified some colleagues who can hopefully anwser your question.

Regards,

Interface

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Steps to communicate to PCF8574 IO expander