DAC_MCP49xx.cpp

/*
 * Microchip MCP4901 / MCP4911 / MCP4921 / MCP4902 / MCP4912 / MCP4922 8/10/12-bit DAC driver
 * Thomas Backman, 2012-07 (made a proper library 2011-07-30, 3 weeks after initial)
 * serenity@exscape.org
 * Support for MCP49x2 (MCP4902, MCP4912, MCP4922) added 2012-08-30,
 * with a patch and testing from Jonas Gruska

 * Code license: BSD/MIT. Whatever; I *prefer* to be credited,
 * and you're *not* allowed to claim you wrote this from scratch.
 * Apart from that, do whatever you feel like. Commercial projects,
 * code modifications, etc.

 Pins used:
 * Arduino pin 11 (for Uno; for Mega: 51) to device SDI (pin 4) - fixed pin
 * Arduino pin 13 (for Uno; for Mega: 52) to device SCK (pin 3) - fixed pin
 * Any digital pin to device LDAC (DAC pin 5)  (except with PortWrite, see README)
 * Any digital pin to device CS   (DAC pin 2)  (as above)
 *
 * Other DAC wirings:
 * Pin 1: VDD, to +5 V
 * Pin 5: LDAC, either to an Arduino pin, or ground to update vout automatically
 * Pin 6: VREF, to +5 V (or some other reference voltage 0 < VREF <= VDD)
 * Pin 7: VSS, to ground
 * Pin 8: vout
 * (Pin 9, for the DFN package only: VSS)

 * Only tested on MCP4901 (8-bit) and MCP4922 (dual 12-bit), but it should work on the others as well.
 * Tested on an Arduino Uno R3.
 */

/*
  Forked by bartoszxkozlowski (Bartosz Kozłowski) in order to add
  Software SPI (https://github.com/MajenkoLibraries/SoftSPI) support.
  Tested on Atmega2560 with MCP4901 module.
*/

#include "DAC_MCP49xx.h"

DAC_MCP49xx::DAC_MCP49xx(DAC_MCP49xx::Model _model, int _sdi_pin, int _sdo_pin, int _sck_pin, int _ss_pin, int _LDAC_pin) : bufferVref(false), gain2x(false), port_write(false), spi_divider(SPI_CLOCK_DIV2), automaticallyLatchDual(true) {
  this->ss_pin = _ss_pin;
  this->LDAC_pin = _LDAC_pin;

  /*
  * MCP49x1 models are single DACs, while MCP49x2 are dual.
  * Apart from that, only the bit width differ between the models.
  */
  switch (_model) {
    case MCP4901:
    case MCP4902:
      bitwidth = 8;
      break;
    case MCP4911:
    case MCP4912:
      bitwidth = 10;
      break;
    case MCP4921:
    case MCP4922:
      bitwidth = 12;
      break;
    default:
      bitwidth = 0;
  }

  pinMode(ss_pin, OUTPUT);  // Ensure that SS is set to SPI master mode
  pinMode(LDAC_pin, OUTPUT);

  digitalWrite(ss_pin, HIGH);    // Unselect the device
  digitalWrite(LDAC_pin, HIGH);  // Un-latch the output

  SSPI.begin(_sdi_pin, _sdo_pin, _sck_pin);
  SSPI.setBitOrder(MSBFIRST);
  SSPI.setDataMode(SPI_MODE0);
  SSPI.setClockDivider(spi_divider);
}

void DAC_MCP49xx::setBuffer(boolean _buffer) {
  this->bufferVref = _buffer;
}

void DAC_MCP49xx::setPortWrite(boolean _port_write) {
  this->port_write = _port_write;
}

// Only relevant for the MCP49x2 dual DACs.
// If set, calling output2() will pull the LDAC pin low automatically,
// which causes the output to change.
// Not required if the LDAC pin is shorted to ground, however in that case,
// there will be a delay between the updating of channel A and channel B.
// If sync is desired, wire the LDAC pin to the Arduino and set this to true.
boolean DAC_MCP49xx::setAutomaticallyLatchDual(bool _latch) {
  automaticallyLatchDual = _latch;
  return _latch;
}

// Sets the gain. These DACs support 1x and 2x gain.
// vout = x/2^n * gain * VREF, where x = the argument to out(), n = number of DAC bits
// Example: with 1x gain, set(100) on a 8-bit (256-step) DAC would give
// an output voltage of 100/256 * VREF, while a gain of 2x would give
// vout = 100/256 * VREF * 2
boolean DAC_MCP49xx::setGain(int _gain) {
  if (_gain == 1) {
    gain2x = false;
    return true;
  } else if (_gain == 2) {
    gain2x = true;
    return true;
  } else
    return false;  // DAC only supports 1x and 2x
}

// Sets the SPI clock frequency. The final frequency will be the
// main Arduino clock divided by the divider selected here.
boolean DAC_MCP49xx::setSPIDivider(int _div) {
  switch (_div) {
    case SPI_CLOCK_DIV2:
    case SPI_CLOCK_DIV4:
    case SPI_CLOCK_DIV8:
    case SPI_CLOCK_DIV16:
    case SPI_CLOCK_DIV32:
    case SPI_CLOCK_DIV64:
    case SPI_CLOCK_DIV128:
      spi_divider = _div;
      SSPI.setClockDivider(_div);
      return true;
    default:
      return false;
  }
}

// Shuts the DAC down. Shutdown current is about 1/50 (typical) of active mode current.
// My measurements say ~160-180 µA active (unloaded vout), ~3.5 µA shutdown.
// Time to settle on an output value increases from ~4.5 µs to ~10 µs, though (according to the datasheet).
void DAC_MCP49xx::shutdown(void) {
  // Drive chip select low
  if (this->port_write)
    PORTB &= 0xfb;  // Clear PORTB pin 2 = arduino pin 10
  else
    digitalWrite(ss_pin, LOW);

  // Sending all zeroes should work, too, but I'm unsure whether there might be a switching time
  // between buffer and gain modes, so we'll send them so that they have the same value once we
  // exit shutdown.
  unsigned short out = (bufferVref << 14) | ((!(gain2x)) << 13);  // gain == 0 means 2x, so we need to invert it
  SSPI.transfer((out & 0xff00) >> 8);
  SSPI.transfer(out & 0xff);

  // Return chip select to high
  if (this->port_write)
    PORTB |= (1 << 2);  // set PORTB pin 2 = arduino pin 10
  else
    digitalWrite(ss_pin, HIGH);
}

// Private function.
// Called by the output* set of functions.
void DAC_MCP49xx::_output(unsigned short data, Channel chan) {
  // Truncate the unused bits to fit the 8/10/12 bits the DAC accepts
  if (this->bitwidth == 12)
    data &= 0xfff;
  else if (this->bitwidth == 10)
    data &= 0x3ff;
  else if (this->bitwidth == 8)
    data &= 0xff;

  // Drive chip select low
  if (this->port_write)
    PORTB &= 0xfb;  // Clear PORTB pin 2 = arduino pin 10
  else
    digitalWrite(ss_pin, LOW);

  // bit 15: 0 for DAC A, 1 for DAC B. (Always 0 for MCP49x1.)
  // bit 14: buffer VREF?
  // bit 13: gain bit; 0 for 1x gain, 1 for 2x (thus we NOT the variable)
  // bit 12: shutdown bit. 1 for active operation
  // bits 11 through 0: data
  uint16_t out = (chan << 15) | (this->bufferVref << 14) | ((!this->gain2x) << 13) | (1 << 12) | (data << (12 - this->bitwidth));

  // Send the command and data bits
  SSPI.transfer((out & 0xff00) >> 8);
  SSPI.transfer(out & 0xff);

  // Return chip select to high
  if (this->port_write)
    PORTB |= (1 << 2);  // set PORTB pin 2 = arduino pin 10
  else
    digitalWrite(ss_pin, HIGH);
}

// For MCP49x1
void DAC_MCP49xx::output(unsigned short data) {
  this->_output(data, CHANNEL_A);
}

// For MCP49x2
void DAC_MCP49xx::outputA(unsigned short data) {
  this->_output(data, CHANNEL_A);
}

// For MCP49x2
void DAC_MCP49xx::outputB(unsigned short data) {
  this->_output(data, CHANNEL_B);
}

// MCP49x2 (dual DAC) only.
// Send a set of new values for the DAC to output in a single function call
void DAC_MCP49xx::output2(unsigned short data_A, unsigned short data_B) {
  this->_output(data_A, CHANNEL_A);
  this->_output(data_B, CHANNEL_B);

  // Update the output, if desired.
  // The reason this is only in the dual-output version is simple: it's mostly useless
  // for the single-output version, as it would make more sense to tie the \LDAC pin
  // to ground, or do it manually. However, there should be a single-call method
  // to update *both* channels in sync, which wouldn't be possible with multiple
  // separate DACs (for which there is latch()).
  if (automaticallyLatchDual) {
    this->latch();
  }
}

// These DACs have a function where you can change multiple DACs at the same
// time: you call output() "sequentially", one DAC at a time, and *then*,
// when they've all received the output data, pull the LDAC pin low on
// all DACs at once. This function pulls the LDAC pin low for long enough
// for the DAC(s) to change the output.
// If this function is undesired, you can simply tie the LDAC pin to ground.
// When tied to ground, you need *NOT* call this function!
void DAC_MCP49xx::latch(void) {
  // The datasheet says CS must return high for 40+ ns before this function
  // is called: no problems, that'd be taken care of automatically, as one
  // clock cycle at 16 MHz is longer... and there'll be a delay of multiple.

  if (LDAC_pin < 0)
    return;

  // We then need to hold LDAC low for at least 100 ns, i.e ~2 clock cycles.

  if (this->port_write) {
    // This gives ~180 ns (three clock cycles, most of which is spent low) of
    // low time on a Uno R3 (16 MHz), measured on a scope to make sure
    PORTD &= ~(1 << 7);  // Uno: digital pin 7; Mega: digital pin 38
    asm volatile("nop");
    PORTD |= (1 << 7);
  } else {
    // This takes far, FAR longer than the above despite no NOP; digitalWrite
    // is SLOW! For comparison: the above takes 180 ns, this takes... 3.8 us,
    // or 3800 ns, 21 times as long - WITHOUT having a delay in there!
    digitalWrite(LDAC_pin, LOW);
    digitalWrite(LDAC_pin, HIGH);
  }
}