Understanding SPI read from slave

[Toby 0]

Hi Folks

 

Ive recently started looking at using the F2802x SPI. For my application I would like to be able to communicate between two F2802x devices a string of 8-bit chars of arbitrary length (+using FIFOs), and I have a few questions.

 

The slave device is able to request read service from the master by means of a GPIO line to the master that the master has configured as an external interrupt.

 

The thing is I am not understanding the steps required for the master to begin a read from the slave.... I checked out the data transfer example (sect 1.5.5) in the SPI ref guide (SPRUG71B) but TBH I didn't really understand what it was trying to convey...

 

I guess the master needs to transmit dummy bytes for every byte that it wants to receive, is that right?

But how should the master "know" how many bytes that should be? Maybe it just keeps going until the slave clears the TALK bit?

 

Thanks

[timotet 44]

Toby

 

I will try to help.

Im no pro at this, although I have used the SPI peripheral successfully.

 

"I guess the master needs to transmit dummy bytes for every byte that it wants to receive, is that right?"

 

Yes thats right

 

"But how should the master "know" how many bytes that should be? Maybe it just keeps going until the slave clears the TALK bit?"

 

Thats your job to establish in software, maybe the last byte of your transmission from the slave could be 0x00 and

in your masters Rx_Isr have it look for that to end the transmission.

Just a thought.

 

good luck