MCP4922.cpp

/*******************************************************************************
*  MCP4922.cpp - Library for driving MCP4922 2 channel DAC using hardware SPI. *
* Created by Helge Nodland, January 1, 2015.								   *
* Released into the public domain.                                             *
*******************************************************************************/



#if defined(ARDUINO) && ARDUINO >= 100
#include "Arduino.h"
#else
#include "WProgram.h"
#endif

#include "MCP4922.h"
#include <SPI.h>


MCP4922::MCP4922(int SDI, int SCK, int CS, int LDAC)
{
 _SDI = SDI;
 _SCK = SCK;
 _CS = CS;
 _LDAC = LDAC;


 pinMode(_SDI,OUTPUT);
 pinMode(_SCK,OUTPUT);
 pinMode(_CS,OUTPUT);
 pinMode(_LDAC,OUTPUT);

}

//************************************************************************
void MCP4922::Set(int A, int B) {
  sendIntValueSPI(A,B);
}


//************************************************************************ 
/*
Bitmasking for setting options in dac:

The four MSB in the Mask 0b0111000000000000 and 0b1111000000000000 is for
setting different options of the DAC setup.

0bX111000000000000 where X is What DAC channel the SPI is writing to.
bit15			   X=0 is writing to channel A.
				   X=1 is writing to channel B.

0b0X11000000000000 where X is Buffered or UnBuffered mode. Buffered uses LDAC 
bit14			   pin to simuttaneous update both channels.
				   UnBuffered I guess is writing outputs directly to DAC 
				   outputs and ignoring LDAC pin.
				   X=0 is UnBuffered.
				   X=1 is Buffered.
				   
0b01x1000000000000 where X is GAIN selector.  
bit13			   X=0 is 2X GAIN.
				   X=1 is 1X GAIN.
				   
0b011X000000000000 where X SHUTDOWN.
bit12			   X=0 OUTPUT is DISABLED on selected channel.
				   X=1 OUTPUT is ENABLED on selected channel.
			
0b0111XXXXXXXXXXXX where X is the 12 bits to be written to the active channel.
bit 11 down to bit 0			

 */
//************************************************************************

void MCP4922::sendIntValueSPI(int A ,int B) {
int channelA = A | 0b0111000000000000;
int channelB = B | 0b1111000000000000;
       
digitalWrite(_CS, LOW);
SPI.transfer(highByte(channelA));
SPI.transfer(lowByte(channelA));
digitalWrite(_CS, HIGH);

__asm__("nop\n\t");
//delay(1);

digitalWrite(_CS, LOW);
SPI.transfer(highByte(channelB));
SPI.transfer(lowByte(channelB));
digitalWrite(_CS, HIGH); 
digitalWrite(_LDAC,LOW);

__asm__("nop\n\t");
//delay(1);

digitalWrite(_LDAC,HIGH);
}