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Problem with communication SPI

 
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tatthang
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Problem with communication SPI
PostPosted: Fri Dec 19, 2008 3:35 am     Reply with quote
I use 16f877a which is master and another 16f877a is slave.
master:
pin A5 (select)


Code:
//master
#define SS_LOW (output_low(pin_A5)) //pin RA5 conected to nSS in 16F877A
#define SS_HIGH (output_high(pin_A5))
void main()
{
  setup_spi(SPI_MASTER|SPI_L_TO_H|SPI_CLK_DIV_4|SPI_SAMPLE_AT_END);   // TODO: USER CODE!!
  delay_ms(100);

while(1)
{
  int rs;
  SS_LOW;
  while (true)
  {
     spi_write(0x55);
     delay_ms(1);
     rs=spi_read();
     delay_ms(1);
     if(rs==0x33)
     {
        portd=0xff;delay_ms(500);
        portd=0;
     }
  }
}
}

//slave
void main()
{
  int kq;
  setup_spi(SPI_SLAVE | SPI_H_TO_L);
  delay_ms(100);
  while(1)
  {
  kq = spi_read();
  delay_ms(1);
  portd=kq;
  delay_ms(500);
  spi_write(0);

}
}


but when i test with proteus, nothing perform on slave's Portd
please show me what problem i face
Thanks guys
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Fri Dec 19, 2008 4:55 pm     Reply with quote
The SPI master needs to output an SCLK signal when it reads a byte
from the slave. In CCS, this is done by giving the spi_read() function
a parameter. Change your master code to this:
Quote:
rs=spi_read(0);

Now you will get the SCLK in the read operation, and you can continue
working on your design.
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