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Queue up SPI TX in Slave Mode

 
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ralpok



Joined: 21 Dec 2005
Posts: 25

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Queue up SPI TX in Slave Mode
PostPosted: Thu Sep 06, 2012 2:00 pm     Reply with quote
I am working on implementing the SPI Slave using a PIC24FV32KA304 on PCWHD 4.134.

What I need to be able to do is queue up two bytes to transmit once the master starts to clock it in.

Code:

#use SPI (FORCE_HW, SPI1, STREAM=HOST, BITS=8, SLAVE, SAMPLE_RISE,IDLE=1)

...

      whichChannel = spi_xfer(HOST,0x11,8);
      whichChannel = spi_xfer(HOST,0x08,8);   


For the above code when I queue both of these up and then the master clocks in 16 clocks, instead of getting a 0x11 and 0x08 I get two copies of the 0x08 byte. How do I queue up these bytes correctly so that I get both once the master starts clocking in the data.

Thanks!
Ttelmah



Joined: 11 Mar 2010
Posts: 19473

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PostPosted: Fri Sep 07, 2012 1:03 am     Reply with quote
Exactly as you would for the RS232.
You implement a software circular buffer, and use int_ssp, to load the next byte from this to the hardware.

Best Wishes
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