DAC2_SPI_Limits.cpp

#include "DAC.h"

void transferDAC2(uint8_t byte0, uint8_t byte1, uint8_t byte2) {
  uint8_t bytes[3];
  bytes[0] = byte0;
  bytes[1] = byte1;
  bytes[2] = byte2;

  // TODO: When done with this investigation, archive the valuable
  // data in a GitHub Gist.

  // SPI_MODE0, FSDO = 1
  //
  // 5 Mbps - output works, input does
  // 15 Mbps - output works, input does, undefined behavior one time
  // 16 Mbps - undefined behavior all times
  // 34 Mbps - output works, input does not

  // SPI_MODE1, FSDO = 0
  //
  // 15 Mbps - output works, input does
  // 16 Mbps - output works, input does
  // 17 Mbps - output works, input does
  // 18 Mbps - output works, input does not
  // 20 Mbps - output works, input does not
  // 34 Mbps - output works, input does not

  // SPI_MODE1, FSDO = 1
  //
  // 15 Mbps - output works, input does
  // 30 Mbps - output works, input does
  // 34 Mbps - output works, input does
  // 35 Mbps - output works, input does not

  // SPI_MODE2, FSDO = 0
  //
  // 5 Mbps  - output works, input does
  // 14 Mbps - output works, input does
  // 15 Mbps - output works, input does
  // 16 Mbps - output works, input does not
  // 18 Mbps - output works, input does not
  // 19 Mbps - output works, input does not
  // 20 Mbps - output works, input does not
  // 40 Mbps - output works, input does not
  //
  // SPI_MODE2, FSDO = 1
  //
  // 5 Mbps - output works, input does
  // 14 Mbps - output works, input does
  // 16 Mbps - output works, input does
  // 20 Mbps - output works, input does
  // 30 Mbps - output works, input does
  // 32 Mbps - output works, input does
  // 33 Mbps - output works, input does
  // 34 Mbps - output works, input does
  // 35 Mbps - output works, input does not
  // 36 Mbps - output works, input does not
  // 40 Mbps - output works, input does not
  SPI.beginTransaction(SPISettings(34 * 1000000, MSBFIRST, SPI_MODE1));
  digitalWrite(CS_DAC2, 0);
  SPI.transfer(bytes, 3);
  digitalWrite(CS_DAC2, 1);
  SPI.endTransaction();

  uint32_t deviceID = 0;
  deviceID |= uint32_t(bytes[1]) << 8;
  deviceID |= uint32_t(bytes[2]);

  Serial.print(deviceID);
  Serial.print(" ");
  Serial.print(deviceID >> 2);
  Serial.println();
}

// Investigate DAC1 next, find its SPI limits.