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SPI problem, please advise

 
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Ken Lim



Joined: 03 Sep 2008
Posts: 1

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SPI problem, please advise
PostPosted: Wed Sep 03, 2008 8:25 am     Reply with quote
Hi, I am using 2 x 16F887 as Master and Slave. I have no problem transmitting data from Master to slave but I can't get data from Slave.

Master code:
I transfer data by:
Code:
output_low(SS_SPI);
spi_write(data);
output_high(SS_SPI);


I recieve data by:
Code:
output_low(SS_SPI);
spi_write(0x00);
slave_data = spi_read();
output_high(SS_SPI);


Am i correct?

Slave code:
I receive data by:
Code:
while(!spi_data_is_in());
{   
      spi_data_recieved = spi_read();
}


I transmit data by:
Code:
spi_write(0x00); //Put data need to send into the output buffer
while(!spi_data_is_in());
{   
      spi_data_recieved = spi_read();
}

Am I correct?

Please advise on this code format.
I will appreciate if any kind soul can pass me his working sample for my reference.

Thanks.
gip_mad



Joined: 23 Aug 2008
Posts: 24
Location: Italy

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PostPosted: Wed Sep 03, 2008 8:49 am     Reply with quote
There are a lot of working examples in the "examples" folder of your compiler...
RLScott



Joined: 10 Jul 2007
Posts: 465

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Re: SPI problem, please advise
PostPosted: Wed Sep 03, 2008 10:04 am     Reply with quote
The CCS library functions are really setup for the master mode only. For example, the function spi_write() probably does more than just load the SSPBUF. But in slave mode that's all you want to do. I suggest that for slave mode you write directly to the SSPBUF register instead of using the CCS library functions. See the 16F887 Microchip datasheet for details.

The code you have written shows that you understand the principles of master and slave mode operation just fine. The only difficulty is knowing exactly what each CCS library function really does. Personally I would not bother using library functions for this, except maybe for the initializations. For everything else, it is easier to talk directly to the registers.
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