Unable to talk to PCA9745B properly

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Unable to talk to PCA9745B properly

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reecedevon
Contributor I

Hello everyone,

I'm currently trying to talk to a PCA9745B without much luck. I'm using an Aardvark to talk to the board, which is just an I2C/SPI device that allows you to send messages directly from your PC to the board. Right now I'm trying to speak via SPI, and every time I write a command to the board (MOSI) I always receive a read (MISO) of the last command I sent. Even when I send a read command I don't actually get read data, I only receive the last command I sent before the read. Why is the board not following the commands even though it seems communication is working? Is there some kind of configuration I need to do to the board to get these messages to be processed? It's as if my messages are just being queued and looped back to me rather than the chip actually handling them. I've verified with a scope as well that the data is sent correctly as per the data sheet. Any help would be seriously appreciated.

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diazmarin09
NXP TechSupport
NXP TechSupport

Hello Reece,

I hope all is great with you.

Could you please share the commands that you are sending to the PCA9745B device?

Are you following the read/write procedures mentioned on chapter 8.2 from datasheet?

Are you considering the CS pin (the active LOW chip select line is used to activate and access the SPI slaves)?

Regards,

David

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