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Simple MCP42xx driver

 
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asmboy



Joined: 20 Nov 2007
Posts: 2116
Location: albany ny

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Simple MCP42xx driver
PostPosted: Mon Aug 27, 2012 4:09 pm     Reply with quote

For MCP4251 and others in the MCP42x1 family DUAL pots
with 0-257 step control - these are used in an audio appliance
and the SPI Lines are up to 6 feet long - with terminators at the far end.
The delay functions are needed ONLY for use with an 18F46K22 running at Fosc 64 Mhz.

There are other features I neither need nor care about - this merely sets the pots accurately and to any step required.
Code:

// #define PLS  pin_a0
// #define PCK  pin_a1
// #define PDI  pin_a2
// write pot simple - DUAL channel MCP 42xx effective
// work is the value from 0 to 257 to send to the pot
// whichpot=0 is A pot  = 1 is B pot

void setMCP42pot(int1 whichpot, unsigned int16 work){

  unsigned int8 i;
  #bit pob = work.15

  // note: even tho a 10 bit field ,
  // bit 9 is always zero as 257 is max arg for the part

  work &=0b0000000111111111;  // clear any value outside 9  bit range
  if (!whichpot) work |=0b0001000000000000;

  output_high(PCK);
  delay_cycles(4);
  output_low(pls);
  delay_cycles(4);
  output_low(PCK);

  for ( i=0; i<16; i++){
      delay_cycles(2);
      if(pob)  output_high(PDI );
      else     output_low(PDI);
      output_high(PCK);
      work <<=1;
      output_low(PCK);
  }
  delay_cycles(2);
  output_high(pls);
  output_low(PCK);
}
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