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SPI INT16 Read/Write Routine

 
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jecottrell



Joined: 16 Jan 2005
Posts: 559
Location: Tucson, AZ

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SPI INT16 Read/Write Routine
PostPosted: Wed Oct 17, 2007 7:35 pm     Reply with quote
In the never ending attempt to get a MAX3100 working. I thought I'd try a bit-bang SPI function and see if it helps at all.

Can anyone offer any suggestions on the following:

http://datasheets.maxim-ic.com/en/ds/MAX3100.pdf

I think I've got the proper edges sampled.

Code:

#byte   PORTC = 0x0F82
#byte   LATC  = 0x0F8B
#byte   LATF  = 0x0F8E
#bit LCL_CS_BIT  = LATF.3   // local MAX3100 chip select
#bit SPI_CLK_PIN = LATC.3   // SPI SCLK
#bit MOSI_PIN    = LATC.5   // SPI MOSI
#bit MISO_PIN    = PORTC.4  // SPI MISO

int16 SSPtransfer16(int16 data_out)
{
   int8 i;
   int16 data_in;
   
   SPI_CLK_PIN = 0;      // direct addressing
   LCL_CS_PIN = 0;
   delay_cycles(2);
   
   for(i=0;i<16;i++)
   {
      SPI_CLK_PIN = 1;
      //----------------------
      // shift data in
      data_in <<= 1;
      if(!MISO_PIN)            // read the MISO pin
         data_in &= ~1;         // bit = 0
      else                  
         data_in |= 1;         // bit = 1
      //----------------------
      // shift data out
      if(bit_test(data_out,15))
         MOSI_PIN = 1;
      else
         MOSI_PIN = 0;
      //----------------------
      SPI_CLK_PIN = 0;
      data_out <<= 1;
   
   }
   delay_cycles(2);
   LCL_CS_PIN = 1;
   return (data_in);
}
jecottrell



Joined: 16 Jan 2005
Posts: 559
Location: Tucson, AZ

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PostPosted: Wed Oct 17, 2007 11:45 pm     Reply with quote
Looks like everything is working except for this part:

Code:
      // shift data in
      data_in <<= 1;
      if(!MISO_PIN)            // read the MISO pin
         data_in &= ~1;         // bit = 0
      else                  
         data_in |= 1;         // bit = 1



The low byte appears to be correct, but the high byte is 0.

Any ideas?

Thanks,

John

EDIT:

I've checked the data by reading it into an array and printing it out, and the data at the pin is correct.
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