LTC2654 - Quad 16-/12-Bit Rail-to-Rail DACs with 10ppm/°C Max Reference

/*!
Linear Technology DC1678A Demonstration Board.
LTC2654: Quad SPI 16-/12-Bit Rail-to-Rail DACs with 10ppm/C Max Reference.

@verbatim
NOTES
  Setup:
   Set the terminal baud rate to 115200 and select the newline terminator.
   The program displays calculated voltages which are based on the voltage
   of the reference used, be it internal or external. A precision voltmeter
   is needed to verify the actual measured voltages against the calculated
   voltage displayed. If an external reference is used, a precision voltage
   source is required to apply the external reference voltage. A
   precision voltmeter is also required to measure the external reference
   voltage. No external power supply is required. Any assembly option
   may be used: DC1678A-A, DC1678A-B, DC1678A-C, DC1678A-D.


  Explanation of Commands:
   1- Select DAC: Select one of four DACs to test : A, B, C, D.

   2- Write to DAC input register: Value is stored in the DAC for updating
      later, allowing multiple channels to be updated at once, either
      through a software "Update All" command or by asserting the LDAC# pin.
      User will be prompted to enter either a code in hex or decimal, or a
      voltage. If a voltage is entered, a code will be calculated based on
      the active scaling and reference parameters - ideal values if no
      calibration was ever stored.

   3- Write and Update: Similar to item 1, but DAC is updated immediately.

   4- Update DAC: Copies the value from the input register into the DAC
      Register. Note that a "write and update" command writes the code to
      BOTH the input register and DAC register, so subsequent "update"
      commands will simply re-copy the same data (no change in output.)

   5- Power Down DAC: Disable DAC output. Power supply current is reduced.
      DAC code present in DAC registers at time of shutdown are preserved.

   6- Set reference mode, either internal or external: Selecting external
      mode prompts for the external reference voltage, which is used directly
      if no individual DAC calibration is stored. The selection and entered
      voltage are stored to EEPROM so it is persistent across reset / power cycles.

   7- Calibrate DAC: Use a precision voltmeter to obtain and enter VOUT
      readings taken with different DAC codes. Set reference mode FIRST,
      as values are stored separately for internal and external reference
      mode. Entries are used to calculate the closest code to send to the
      DAC to achieve an entered voltage.

   8- Enable / Disable calibration: Switch between stored calibration
      values and defaults. Calibration parameters are stored separately for
      internal and external reference modes. Ideal calibration will be used
      if the calibration parameter valid key is not set.

USER INPUT DATA FORMAT:
 decimal : 1024
 hex     : 0x400
 octal   : 02000  (leading 0 "zero")
 binary  : B10000000000
 float   : 1024.0

@endverbatim

http://www.linear.com/product/LTC2654

http://www.linear.com/product/LTC2654#demoboards

REVISION HISTORY
$Revision: 1884 $
$Date: 2013-08-15 10:09:10 -0700 (Thu, 15 Aug 2013) $

Copyright (c) 2013, Linear Technology Corp.(LTC)
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright notice, this
   list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright notice,
   this list of conditions and the following disclaimer in the documentation
   and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

The views and conclusions contained in the software and documentation are those
of the authors and should not be interpreted as representing official policies,
either expressed or implied, of Linear Technology Corp.

The Linear Technology Linduino is not affiliated with the official Arduino team.
However, the Linduino is only possible because of the Arduino team's commitment
to the open-source community.  Please, visit http://www.arduino.cc and
http://store.arduino.cc , and consider a purchase that will help fund their
ongoing work.
 */

/*! @file
    @ingroup LTC2654
*/

#include <Arduino.h>
#include <stdint.h>
#include "Linduino.h"
#include "LT_SPI.h"
#include "UserInterface.h"
#include "LT_I2C.h"
#include "QuikEval_EEPROM.h"
#include "LTC2654.h"
#include <SPI.h>
#include <Wire.h>

#define EEPROM_CAL_KEY_INT  0x5678          //!< Calibration associated with internal reference
#define EEPROM_CAL_KEY_EXT  0x9ABC          //!< Calibration associated with external reference

// DAC Reference State
// Could have been zero or 1, this allows you to use the
// variable "reference_mode" as the command argument to a write
#define REF_INTERNAL LTC2654_CMD_INTERNAL_REFERENCE   //!< Stored reference state is Internal
#define REF_EXTERNAL LTC2654_CMD_EXTERNAL_REFERENCE   //!< Stored reference state is External

// EEPROM memory locations
#define STORED_REF_STATE_BASE     EEPROM_CAL_STATUS_ADDRESS     //!< Base address of the stored reference state
#define INT_CAL_VALID_BASE        STORED_REF_STATE_BASE + 2     //!< Base address of the "internal ref calibration valid" flag
#define INT_CAL_PARAMS_BASE       INT_CAL_VALID_BASE + 2        //!< Base address of the internal ref calibration parameters
#define EXT_CAL_VALID_BASE        INT_CAL_PARAMS_BASE + 32      //!< Base address of the "external ref calibration valid" flag
#define EXT_CAL_PARAMS_BASE       EXT_CAL_VALID_BASE + 2        //!< Base address of the external ref calibration parameters
#define EXT_REF_V_BASE            EXT_CAL_PARAMS_BASE + 32      //!< Base address of the stored external reference voltage

// Function Declaration
int8_t restore_calibration();               // Read the DAC calibration from EEPROM, Return 1 if successful, 0 if not
void store_calibration();                   // Store the DAC calibration to the EEPROM
void print_title();                         // Print the title block
void print_prompt(int16_t selected_dac);    // Prompt the user for an input command
int16_t prompt_voltage_or_code();
uint16_t get_voltage(float LTC2654_lsb, int16_t LTC2654_offset);
uint16_t get_code();
void calibrate_dac(uint8_t index);       // Calibrate the selected DAC using a voltmeter. The routine does a linear curve fit given two data points.

void menu_1_select_dac(int16_t *selected_dac);
void menu_2_write_to_input_register(int16_t selected_dac);
void menu_3_write_and_update_dac(int16_t selected_dac);
void menu_4_update_power_up_dac(int16_t selected_dac);
void menu_5_power_down_dac(int16_t selected_dac);
void menu_6_set_reference_mode();         // Int, ext, if ext, prompt for voltage
void menu_7_calibrate_dacs();
void menu_8_enable_calibration();

// Global variables
static uint8_t demo_board_connected;   //!< Set to 1 if the board is connected
static uint8_t shift_count = 0;        //!< The data align shift count. For 16-bit=0, for 12-bits=4
static uint8_t reference_mode;         //!< Tells whether to set internal or external reference

// Global calibration variables
static float reference_voltage;    //!< Reference voltage, either internal or external
static int16_t LTC2654_offset[5];      //!< DAC offset - index 4 for "all DACs"
static float LTC2654_lsb[5];           //!< The LTC2654 lsb - index 4 for "all DACs"

// Constants

//! Lookup table for DAC address. Allows the "All DACs" address to be indexed right after DAC D in loops.
//! This technique is very useful for devices with non-monotonic channel addresses.
const uint8_t address_map[5] = {LTC2654_DAC_A, LTC2654_DAC_B, LTC2654_DAC_C, LTC2654_DAC_D, LTC2654_DAC_ALL};  //!< Map entered option 0..2 to DAC address

//! Used to keep track to print voltage or print code
enum {
        PROMPT_VOLTAGE = 0, /**< 0 */ 
        PROMPT_CODE = 1     /**< 1 */
     }; 

//! Initialize Linduino
void setup()
// Setup the program
{
  char demo_name[] = "DC1678";  // Demo Board Name stored in QuikEval EEPROM
  quikeval_SPI_init();          // Configure the spi port for 4MHz SCK
  quikeval_SPI_connect();       // Connect SPI to main data port
  quikeval_I2C_init();          // Configure the EEPROM I2C port for 100kHz
  Serial.begin(115200);         // Initialize the serial port to the PC
  print_title();
  demo_board_connected = discover_demo_board(demo_name);
  if (demo_board_connected)
  {
    restore_calibration();
    print_prompt(0);
  }
}

//! Repeats Linduino loop
void loop()
{
  int16_t user_command;
  static  int16_t selected_dac = 0;     // The selected DAC to be updated (0=A, 1=B ... 5=All).  Initialized to "A".
  // The main control loop
  if (demo_board_connected)             // Do nothing if the demo board is not connected
  {
    if (Serial.available())             // Check for user input
    {
      user_command = read_int();        // Read the user command
      Serial.println(user_command);
      Serial.flush();
      switch (user_command)
      {
        case 1:
          menu_1_select_dac(&selected_dac);
          break;
        case 2:
          menu_2_write_to_input_register(selected_dac);
          break;
        case 3:
          menu_3_write_and_update_dac(selected_dac);
          break;
        case 4:
          menu_4_update_power_up_dac(selected_dac);
          break;
        case 5:
          menu_5_power_down_dac(selected_dac);
          break;
        case 6:
          menu_6_set_reference_mode(); // Int, ext, if ext, prompt for voltage
          restore_calibration();
          break;
        case 7:
          menu_7_calibrate_dacs();
          restore_calibration();
          break;
        case 8:
          menu_8_enable_calibration();
          restore_calibration();
          break;
        default:
          Serial.println("Incorrect Option");
          break;
      }
      Serial.println("\n*****************************************************************");
      print_prompt(selected_dac);
    }
  }
}

// Function Definitions

//! Select which DAC to operate on
void menu_1_select_dac(int16_t *selected_dac)
{
  // Select a DAC to operate on
  Serial.print("Select DAC to operate on (0=A, 1=B, 2=C, 3=D, 4=All)");
  *selected_dac = read_int();
  if (*selected_dac == 4)
    Serial.println("All");
  else
    Serial.println(*selected_dac);
}

//! Write data to input register, but do not update DAC output
void menu_2_write_to_input_register(int16_t selected_dac)
{
  uint16_t dac_code;

  if (prompt_voltage_or_code() == PROMPT_VOLTAGE)
    dac_code = get_voltage(LTC2654_lsb[selected_dac], LTC2654_offset[selected_dac]);
  else
    dac_code = get_code();

  LTC2654_write(LTC2654_CS, LTC2654_CMD_WRITE, address_map[selected_dac], dac_code << shift_count);
}

//!Write data to DAC register (which updates output immediately)
void menu_3_write_and_update_dac(int16_t selected_dac)
{
  uint16_t dac_code;

  if (prompt_voltage_or_code() == PROMPT_VOLTAGE)
    dac_code = get_voltage(LTC2654_lsb[selected_dac], LTC2654_offset[selected_dac]);
  else
    dac_code = get_code();

  LTC2654_write(LTC2654_CS,LTC2654_CMD_WRITE_UPDATE, address_map[selected_dac], dac_code << shift_count);
}

//! Update DAC with data that is stored in input register, power up if sleeping
void menu_4_update_power_up_dac(int16_t selected_dac)
{
  // Update DAC
  LTC2654_write(LTC2654_CS,LTC2654_CMD_UPDATE, address_map[selected_dac], 0x0000);
}

//! Power down DAC
void menu_5_power_down_dac(int16_t selected_dac)
{
  // Power down DAC
  LTC2654_write(LTC2654_CS,LTC2654_CMD_POWER_DOWN, address_map[selected_dac], 0x0000);
}

//! Set reference mode and store to EEPROM
void menu_6_set_reference_mode(void) // int, ext, if ext, prompt for voltage
{
  int16_t user_input;
  Serial.println("Select reference mode - 0 for Internal, 1 for External");
  user_input = read_int();
  if (user_input == 1)
  {
    reference_mode = REF_EXTERNAL;
    Serial.println("External reference mode; enter external reference voltage");
    reference_voltage = read_float();
    Serial.print(reference_voltage, 5);
    Serial.println("V");
    eeprom_write_float(EEPROM_I2C_ADDRESS, reference_voltage, EXT_REF_V_BASE);
  }
  else
  {
    reference_mode = REF_INTERNAL;
    Serial.println("Internal reference mode selected");
  }
  Serial.println("Writing reference mode to EEPROM\n\n");
  eeprom_write_byte(EEPROM_I2C_ADDRESS, reference_mode, STORED_REF_STATE_BASE);
}

//! Calibrate all DACs by measuring two known outputs
void menu_7_calibrate_dacs()
{
  // Calibrate the DACs using a multimeter
  uint8_t i;
  for (i = 0; i < 4; i++)
  {
    calibrate_dac(i);   // Run calibration routine
  }
  store_calibration();
}

//! Enable / Disable calibration. Use with caution - behavior is undefined if you enable calibration and an actual
//! calibration cycle has not been performed.
void menu_8_enable_calibration()
{
  int16_t user_input;
  Serial.println(F("\n\nSelect option -  0: Enable Internal, 1: Disable Internal, 2: Enable External, 3: Disable External"));
  user_input = read_int();
  switch (user_input)
  {
    case 0:
      Serial.println(F("Enabling Internal Cal Params"));
      eeprom_write_int16(EEPROM_I2C_ADDRESS, EEPROM_CAL_KEY, INT_CAL_VALID_BASE);
      break;
    case 1:
      Serial.println(F("Disabling Internal Cal Params"));
      eeprom_write_int16(EEPROM_I2C_ADDRESS, 0x0000, INT_CAL_VALID_BASE);
      break;
    case 2:
      Serial.println(F("Enabling External Cal Params"));
      eeprom_write_int16(EEPROM_I2C_ADDRESS, EEPROM_CAL_KEY, EXT_CAL_VALID_BASE);
      break;
    case 3:
      Serial.println(F("Disabling External Cal Params"));
      eeprom_write_int16(EEPROM_I2C_ADDRESS, 0x0000, EXT_CAL_VALID_BASE);
      break;
  }
}

//! Read stored calibration parameters from nonvolatile EEPROM on demo board
//! @return Return 1 if successful, 0 if not
int8_t restore_calibration()
// Read the DAC calibration from EEPROM
{
  int16_t intvalid, extvalid;
  uint8_t i, eeaddr;
  float dac_count;                                  // The number of codes, 4096 for 12 bits, 65536 for 16 bits

  Serial.println(F("\n\nReading Calibration parameters from EEPROM..."));
  float full_scale; // To avoid confusion - in internal ref mode, FS=Vref, in ext mode, FS=2*Vref
  // Read the cal keys from the EEPROM.
  eeprom_read_int16(EEPROM_I2C_ADDRESS, &intvalid, INT_CAL_VALID_BASE);
  eeprom_read_int16(EEPROM_I2C_ADDRESS, &extvalid, EXT_CAL_VALID_BASE);
  // Read the stored reference state
  eeprom_read_byte(EEPROM_I2C_ADDRESS, (char *) &reference_mode, STORED_REF_STATE_BASE);
  // Read external ref V unconditionally, overwrite with defaults if no cal found
  eeprom_read_float(EEPROM_I2C_ADDRESS, &reference_voltage, EXT_REF_V_BASE);

  if (reference_mode == REF_EXTERNAL)
  {
    Serial.println(F("Restored external ref. Voltage:"));
    Serial.println(reference_voltage, 5);
  }
  else  // EITHER reference is set to internal, OR not programmed in which case default to internal
  {
    reference_mode = REF_INTERNAL; // Redundant if already set
    Serial.println("Internal reference mode set");
  }

  // Write the reference mode to the DAC right away
  LTC2654_write(LTC2654_CS,reference_mode, 0x0F, 0x0000);

  // Set up default values, shift count, DAC count
  // Calibration parameters MAY be changed next, if match
  // between reference mode and stored calibration
  full_scale = reference_voltage * 2.0; // If external ref mode, this applies.
  switch (demo_board.option)
  {
    case 'A':
      // LTC2654CUF-L16, 16-bits, 2.5V full scale
      shift_count = 0;
      if (reference_mode == REF_INTERNAL) full_scale = 2.5;
      dac_count = 65536;
      break;
    case 'B':
      // LTC2654CUF-H16, 16-bits, 4.096V full scale
      shift_count = 0;
      if (reference_mode == REF_INTERNAL) full_scale = 4.096;
      dac_count = 65536;
      break;
    case 'C':
      // LTC2654CUF-L12, 12-bits, 2.5V full scale
      shift_count = 4;
      if (reference_mode == REF_INTERNAL) full_scale = 2.5;
      dac_count = 4096;
      break;
    case 'D':
      // LTC2654CUF-H12, 12-bits, 4.096V full scale
      shift_count = 4;
      if (reference_mode == REF_INTERNAL) full_scale = 4.096;
      dac_count = 4096;
      break;
  }

  for (i = 0; i <= 4; i++)
  {
    LTC2654_offset[i] = 0;
    LTC2654_lsb[i] = full_scale / dac_count;
  }

  // Restore calibration IF reference mode matches stored calibration
  eeaddr = 0;   // Assume no calibration present or mismatch between cal and reference mode

  if ((intvalid == EEPROM_CAL_KEY) && (reference_mode == REF_INTERNAL))
  {
    eeaddr = INT_CAL_PARAMS_BASE;
    Serial.println(F("Found internal calibration, restoring...)"));
  }
  else if ((extvalid == EEPROM_CAL_KEY) && (reference_mode == REF_EXTERNAL))
  {
    eeaddr = EXT_CAL_PARAMS_BASE;
    Serial.println(F("Found external calibration, restoring...)"));
  }
  else Serial.println(F("Calibration not found for this\nreference mode, using ideal calibration"));

  if (eeaddr != 0) // If cal key was enabled and reference mode is correct, read offset and lsb
  {
    eeprom_read_int16(EEPROM_I2C_ADDRESS, &LTC2654_offset[0], eeaddr);
    eeprom_read_int16(EEPROM_I2C_ADDRESS, &LTC2654_offset[1], eeaddr + 2);
    eeprom_read_int16(EEPROM_I2C_ADDRESS, &LTC2654_offset[2], eeaddr + 4);
    eeprom_read_int16(EEPROM_I2C_ADDRESS, &LTC2654_offset[3], eeaddr + 6);
    eeprom_read_float(EEPROM_I2C_ADDRESS, &LTC2654_lsb[0], eeaddr + 8);
    eeprom_read_float(EEPROM_I2C_ADDRESS, &LTC2654_lsb[1], eeaddr + 12);
    eeprom_read_float(EEPROM_I2C_ADDRESS, &LTC2654_lsb[2], eeaddr + 16);
    eeprom_read_float(EEPROM_I2C_ADDRESS, &LTC2654_lsb[3], eeaddr + 20);
    LTC2654_offset[4] = LTC2654_offset[0]; // Copy cal value for DAC A to cal value for
    LTC2654_lsb[4] = LTC2654_lsb[0];       // DAC ALL
    Serial.println("Calibration Restored");
  }
  for (i=0; i<=4; ++i)
  {
    Serial.print("DAC ");
    Serial.print((char) ('A' + i));
    Serial.print(" offset: ");
    Serial.print(LTC2654_offset[i]);
    Serial.print(" , lsb: ");
    Serial.print(LTC2654_lsb[i]*1000, 4);
    Serial.println(" mv");
  }
  Serial.println("(DAC E applies to ALL DACs selections)");
  if (eeaddr != 0) return (1);
  return (0);
}

//! Store measured calibration parameters to nonvolatile EEPROM on demo board
void store_calibration()
// Store the DAC calibration to the EEPROM
{
  uint8_t eeaddr;
  if (reference_mode == REF_INTERNAL)
  {
    eeprom_write_int16(EEPROM_I2C_ADDRESS, EEPROM_CAL_KEY, INT_CAL_VALID_BASE);
    eeaddr = INT_CAL_PARAMS_BASE;
  }
  else
  {
    eeprom_write_int16(EEPROM_I2C_ADDRESS, EEPROM_CAL_KEY, EXT_CAL_VALID_BASE);
    eeaddr = EXT_CAL_PARAMS_BASE;
  }

  eeprom_write_int16(EEPROM_I2C_ADDRESS, LTC2654_offset[0], eeaddr);        // Offset
  eeprom_write_int16(EEPROM_I2C_ADDRESS, LTC2654_offset[1], eeaddr + 2);
  eeprom_write_int16(EEPROM_I2C_ADDRESS, LTC2654_offset[2], eeaddr + 4);
  eeprom_write_int16(EEPROM_I2C_ADDRESS, LTC2654_offset[3], eeaddr + 6);
  eeprom_write_float(EEPROM_I2C_ADDRESS, LTC2654_lsb[0], eeaddr + 8);      // lsb
  eeprom_write_float(EEPROM_I2C_ADDRESS, LTC2654_lsb[1], eeaddr + 12);
  eeprom_write_float(EEPROM_I2C_ADDRESS, LTC2654_lsb[2], eeaddr + 16);
  eeprom_write_float(EEPROM_I2C_ADDRESS, LTC2654_lsb[3], eeaddr + 20);
  Serial.println(F("Calibration Stored to EEPROM"));
}

//! Prompt user to enter a voltage or digital code to send to DAC
//! @returns user input
int16_t prompt_voltage_or_code()
{
  int16_t user_input;
  Serial.print(F("Type 1 to enter voltage, 2 to enter code:"));
  Serial.flush();
  user_input = read_int();
  Serial.println(user_input);

  if (user_input != 2)
    return(PROMPT_VOLTAGE);
  else
    return(PROMPT_CODE);
}

//! Get voltage from user input, calculate DAC code based on lsb, offset
//! @returns the DAC code
uint16_t get_voltage(float LTC2654_lsb, int16_t LTC2654_offset)
{
  float dac_voltage;

  Serial.print(F("Enter Desired DAC output voltage: "));
  dac_voltage = read_float();
  Serial.print(dac_voltage);
  Serial.println(" V");
  Serial.flush();
  return(LTC2654_voltage_to_code(dac_voltage, LTC2654_lsb, LTC2654_offset));
}

//! Get code to send to DAC directly, in decimal, hex, or binary
//! @return code from user
uint16_t get_code()
{
  uint16_t returncode;
  Serial.println("Enter Desired DAC Code");
  Serial.print("(Format 32768, 0x8000, 0100000, or B1000000000000000): ");
  returncode = (uint16_t) read_int();
  Serial.print("0x");
  Serial.println(returncode, HEX);
  Serial.flush();
  return(returncode);
}

//! Prints the title block when program first starts.
void print_title()
{
  Serial.println("");
  Serial.println(F("*****************************************************************"));
  Serial.println(F("* DC1678 Demonstration Program                                  *"));
  Serial.println(F("*                                                               *"));
  Serial.println(F("* This program demonstrates how to send data to the LTC2654     *"));
  Serial.println(F("* quad 16/12-bit DAC found on the DC1678 demo board.            *"));
  Serial.println(F("*                                                               *"));
  Serial.println(F("* Set the baud rate to 115200 and select the newline terminator.*"));
  Serial.println(F("*                                                               *"));
  Serial.println(F("*****************************************************************"));
}

//! Prints main menu.
void print_prompt(int16_t selected_dac)
{
  Serial.println(F("\nCommand Summary:"));
  Serial.println(F("  1-Select DAC"));
  Serial.println(F("  2-Write to input register (no update)"));
  Serial.println(F("  3-Write and update DAC"));
  Serial.println(F("  4-Update / power up DAC"));
  Serial.println(F("  5-Power down DAC"));
  Serial.println(F("  6-Set reference mode"));
  Serial.println(F("  7-Calibrate DAC"));
  Serial.println(F("  8-Enable / Disable calibration"));

  Serial.println("\nPresent Values:");
  Serial.print("  Selected DAC: ");
  if (selected_dac != 4)
    Serial.println((char) (selected_dac + 0x41));
  else
    Serial.println("All");
  Serial.print("  DAC Reference: ");
  if (reference_mode == REF_INTERNAL)
    Serial.println("Internal");
  else
  {
    Serial.print(F("External "));
    Serial.print(reference_voltage, 5);
    Serial.println(F("V reference, please verify"));
    Serial.print(F("Enter a command:"));

  }
  Serial.flush();
}

//! Calibrate the selected DAC using a voltmeter. The routine
//! does a linear curve fit given two data points.
void calibrate_dac(uint8_t index)
{
  uint16_t code1 = 0x0200;                            //! Calibration code 1
  uint16_t code2 = 0xFFFF;                            //! Calibration code 2
  float voltage1;                                     //! Calibration voltage 1
  float voltage2;                                     //! Calibration voltage 2
  Serial.println("");
  Serial.print("Calibrating DAC ");
  Serial.println((char) (0x41 + index));
  // Left align 12-bit code1 to 16 bits & write to DAC
  LTC2654_write(LTC2654_CS,LTC2654_CMD_WRITE_UPDATE, index, code1 << shift_count);
  Serial.print("DAC code set to 0x");
  Serial.println(code1, HEX);
  Serial.print("Enter measured DAC voltage:");
  voltage1 = read_float();
  Serial.print(voltage1, 6);
  Serial.println(" V");
  // Left align 12-bit code2 to 16 bits & write to DAC
  LTC2654_write(LTC2654_CS,LTC2654_CMD_WRITE_UPDATE, index, code2 << shift_count);
  Serial.print("DAC code set to 0x");
  Serial.println(code2, HEX);
  Serial.print("Enter measured DAC voltage:");
  voltage2 = read_float();
  Serial.print(voltage2, 6);
  Serial.println(" V");
  LTC2654_calibrate(code1, code2, voltage1, voltage2, &LTC2654_lsb[index], &LTC2654_offset[index]);
}

/*!
LTC2654: Quad SPI 16-/12-Bit Rail-to-Rail DACs with 10ppm/C Max Reference

@verbatim

The LTC2654 is a family of quad 16-/12-bit rail-to-rail DACs with integrated 
10ppm/C maximum reference. The DACs have built-in high performance, rail-to- 
rail, output buffers and are guaranteed monotonic. The LTC2654-L has a full- 
scale output of 2.5V with the integrated reference and operates from a single 
2.7V to 5.5V supply. The LTC2654-H has a full-scale output of 4.096V with the 
integrated reference and operates from a 4.5V to 5.5V supply. Each DAC can also 
operate with an external reference, which sets the full-scale output to 2 times 
the external reference voltage. These DACs communicate via a SPI/MICROWIRE 
compatible 4-wire serial interface which operates at clock rates up to 50MHz. 
The LTC2654 incorporates a power-on reset circuit that is controlled by the 
PORSEL pin. If PORSEL is tied to GND, the DACs reset to zero-scale. If PORSEL is 
tied to VCC, the DACs reset to mid-scale. 

@endverbatim

http://www.linear.com/product/LTC2654

http://www.linear.com/product/LTC2654#demoboards

REVISION HISTORY
$Revision: 1827 $
$Date: 2013-08-08 08:58:49 -0700 (Thu, 08 Aug 2013) $

Copyright (c) 2013, Linear Technology Corp.(LTC)
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright notice, this
   list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright notice,
   this list of conditions and the following disclaimer in the documentation
   and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

The views and conclusions contained in the software and documentation are those
of the authors and should not be interpreted as representing official policies,
either expressed or implied, of Linear Technology Corp.

The Linear Technology Linduino is not affiliated with the official Arduino team.
However, the Linduino is only possible because of the Arduino team's commitment
to the open-source community.  Please, visit http://www.arduino.cc and
http://store.arduino.cc , and consider a purchase that will help fund their
ongoing work.
*/

//! @defgroup LTC2654 LTC2654: Quad SPI 16-/12-Bit Rail-to-Rail DACs with 10ppm/C Max Reference

/*! @file
    @ingroup LTC2654
    Library for LTC2654  Quad SPI 16-/12-Bit Rail-to-Rail DACs with 10ppm/C Max Reference
*/

#include <stdint.h>
#include <math.h>
#include <Arduino.h>
#include "Linduino.h"
#include "LT_SPI.h"
#include "LTC2654.h"
#include <SPI.h>

// Write the 16-bit dac_code to the LTC2654
void LTC2654_write(uint8_t cs, uint8_t dac_command, uint8_t dac_address, uint16_t dac_code)
{
  uint8_t data_array[3], rx_array[3];
  LT_union_int16_2bytes data;

  data.LT_uint16 = dac_code;

  data_array[2] = dac_command | dac_address;
  data_array[1] = data.LT_byte[1];
  data_array[0] =data.LT_byte[0];

  spi_transfer_block(cs, data_array, rx_array, (uint8_t) 3);
}

// Calculate a LTC2654 DAC code given the desired output voltage and DAC address (0-3)
uint16_t LTC2654_voltage_to_code(float dac_voltage, float LTC2654_lsb, int16_t LTC2654_offset)
{
  int32_t dac_code;
  float float_code;
  float_code = dac_voltage / LTC2654_lsb;                                                             //! 1) Calculate the DAC code
  float_code = (float_code > (floor(float_code) + 0.5)) ? ceil(float_code) : floor(float_code);       //! 2) Round
  dac_code = (int32_t)float_code - LTC2654_offset;                                                    //! 3) Subtract offset
  if (dac_code < 0)                                                                                   //! 4) If DAC code < 0, Then DAC code = 0
    dac_code = 0;
  return ((uint16_t)dac_code);                                                                        //! 5) Cast DAC code as uint16_t
}

// Calculate the LTC2654 DAC output voltage given the DAC code and DAC address (0-3)
float LTC2654_code_to_voltage(uint16_t dac_code, float LTC2654_lsb, int16_t LTC2654_offset)
{
  float dac_voltage;
  dac_voltage = ((float)(dac_code + LTC2654_offset)* LTC2654_lsb);                                    //! 1) Calculates the dac_voltage
  return (dac_voltage);
}

// Calculate the LTC2654 offset and LSB voltage given two measured voltages and their corresponding codes
void LTC2654_calibrate(uint16_t dac_code1, uint16_t dac_code2, float voltage1, float voltage2, float *LTC2654_lsb, int16_t *LTC2654_offset)
{
  float temp_offset;
  *LTC2654_lsb = (voltage2 - voltage1) / ((float) (dac_code2 - dac_code1));                           //! 1) Calculate the LSB
  temp_offset = voltage1/(*LTC2654_lsb) - dac_code1;                                                  //! 2) Calculate the offset
  temp_offset = (temp_offset > (floor(temp_offset) + 0.5)) ? ceil(temp_offset) : floor(temp_offset);  //! 3) Round offset
  *LTC2654_offset = (int16_t)temp_offset;                                                             //! 4) Cast as int16_t
}

/*!
LTC2654: Quad SPI 16-/12-Bit Rail-to-Rail DACs with 10ppm/C Max Reference

@verbatim

The LTC2654 is a family of quad 16-/12-bit rail-to-rail DACs with integrated 
10ppm/C maximum reference. The DACs have built-in high performance, rail-to- 
rail, output buffers and are guaranteed monotonic. The LTC2654-L has a full- 
scale output of 2.5V with the integrated reference and operates from a single 
2.7V to 5.5V supply. The LTC2654-H has a full-scale output of 4.096V with the 
integrated reference and operates from a 4.5V to 5.5V supply. Each DAC can also 
operate with an external reference, which sets the full-scale output to 2 times 
the external reference voltage. These DACs communicate via a SPI/MICROWIRE 
compatible 4-wire serial interface which operates at clock rates up to 50MHz. 
The LTC2654 incorporates a power-on reset circuit that is controlled by the 
PORSEL pin. If PORSEL is tied to GND, the DACs reset to zero-scale. If PORSEL is 
tied to VCC, the DACs reset to mid-scale. 

SPI DATA FORMAT (MSB First):

24-Bit Load Sequence:

             Byte #1                   Byte #2                         Byte #3
             Command                   MSB                             LSB
LTC2654-16 : C3 C2 C1 C0 A3 A2 A1 A0   D15 D14 D13 D12 D11 D10 D9 D8   D7 D6 D5 D4 D3 D2 D1 D0
LTC2654-12 : C3 C2 C1 C0 A3 A2 A1 A0   D11 D10 D9  D8  D7  D6  D5 D4   D3 D2 D1 D0 X  X  X  X

32-Bit Load Sequence:

             Byte #1                   Byte #2                   Byte #3                         Byte #4
             Command                   MSB                                                       LSB
LTC2654-16 : X  X  X  X  X  X  X  X    C3 C2 C1 C0 A3 A2 A1 A0   D15 D14 D13 D12 D11 D10 D9 D8   D7 D6 D5 D4 D3 D2 D1 D0
LTC2654-12 : X  X  X  X  X  X  X  X    C3 C2 C1 C0 A3 A2 A1 A0   D11 D10 D9  D8  D7  D6  D5 D4   D3 D2 D1 D0 X  X  X  X

Cx   : DAC Command Code
Ax   : DAC Address (0=DACA, 1=DACB, 2=DACC, 3=DACD, 0xFF=All DACs)
Dx   : DAC Data Bits
X    : Don't care


Example Code:

Set DAC A to to 2V for 16-bit DAC.

    shift_count = 0;    // 16-bit DAC does not have to be shifted
    dac_voltage = 2.0;  // Sets dac voltage variable to 2v

    dac_code = LTC2654_voltage_to_code(dac_voltage, LTC2654_lsb, LTC2654_offset);       // Calculate DAC code from voltage, lsb, and offset
    LTC2654_write(LTC2654_CS, LTC2654_CMD_WRITE_UPDATE, LTC2654_DAC_A, dac_code << shift_count);    // Set DAC A with DAC code

@endverbatim

http://www.linear.com/product/LTC2654

http://www.linear.com/product/LTC2654#demoboards

REVISION HISTORY
$Revision: 1807 $
$Date: 2013-07-29 13:06:06 -0700 (Mon, 29 Jul 2013) $

Copyright (c) 2013, Linear Technology Corp.(LTC)
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright notice, this
   list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright notice,
   this list of conditions and the following disclaimer in the documentation
   and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

The views and conclusions contained in the software and documentation are those
of the authors and should not be interpreted as representing official policies,
either expressed or implied, of Linear Technology Corp.

The Linear Technology Linduino is not affiliated with the official Arduino team.
However, the Linduino is only possible because of the Arduino team's commitment
to the open-source community.  Please, visit http://www.arduino.cc and
http://store.arduino.cc , and consider a purchase that will help fund their
ongoing work.
*/

/*! @file
    @ingroup LTC2654
    Header for LTC2654  Quad SPI 16-/12-Bit Rail-to-Rail DACs with 10ppm/C Max Reference
*/

#ifndef LTC2654_H
#define LTC2654_H

#include <SPI.h>

//! Define the SPI CS pin
#ifndef LTC2654_CS
#define LTC2654_CS QUIKEVAL_CS
#endif

//! @name LTC2654 Command Codes
//!@{
//! OR'd together with the DAC address to form the command byte
#define  LTC2654_CMD_WRITE               0x00  //!< Write to input register n
#define  LTC2654_CMD_UPDATE              0x10  //!< Update (power up) DAC register n
#define  LTC2654_CMD_WRITE_UPDATE_ALL    0x20  //!< Write to input register n, update (power up) all
#define  LTC2654_CMD_WRITE_UPDATE        0x30  //!< Write to input register n, update (power up) all
#define  LTC2654_CMD_POWER_DOWN          0x40  //!< Power down n
#define  LTC2654_CMD_POWER_DOWN_ALL      0x50  //!< Power down chip (all DACs and reference)
#define  LTC2654_CMD_INTERNAL_REFERENCE  0x60  //!< Select internal reference (power up reference)
#define  LTC2654_CMD_EXTERNAL_REFERENCE  0x70  //!< Select external reference (power down internal reference)
#define  LTC2654_CMD_NO_OPERATION        0xF0  //!< No operation
//!@}

//! @name LTC2654 DAC addresses
//! @{
//! Which DAC to operate on
#define  LTC2654_DAC_A     0x00
#define  LTC2654_DAC_B     0x01
#define  LTC2654_DAC_C     0x02
#define  LTC2654_DAC_D     0x03
#define  LTC2654_DAC_ALL   0x0F
//! @}

//! Write the 16-bit dac_code to the LTC2654
//! @return Void
void LTC2654_write(uint8_t cs,                            //!< Chip Select Pin
                   uint8_t dac_command,                   //!< Command Nibble, left-justified, lower nibble set to zero
                   uint8_t dac_address,                   //!< DAC Address Nibble, right justified, upper nibble set to zero
                   uint16_t dac_code                      //!< 16-bit DAC code
                  );

//! Calculate a LTC2654 DAC code given the desired output voltage and DAC address (0-3)
//! @return The 16-bit code to send to the DAC
uint16_t LTC2654_voltage_to_code(float dac_voltage,       //!< Voltage to send to DAC
                                 float LTC2654_lsb,       //!< LSB value (volts)
                                 int16_t LTC2654_offset   //!< Offset (volts)
                                );

//! Calculate the LTC2654 DAC output voltage given the DAC code, offset, and LSB value
//! @return Calculated voltage
float LTC2654_code_to_voltage(uint16_t dac_code,          //!< DAC code
                              float LTC2654_lsb,          //!< LSB value (volts)
                              int16_t LTC2654_offset      //!< Offset (volts)
                             );

//! Calculate the LTC2654 offset and LSB voltage given two measured voltages and their corresponding codes
//! @return Void
void LTC2654_calibrate(uint16_t dac_code1,                //!< First DAC code
                       uint16_t dac_code2,                //!< Second DAC code
                       float voltage1,                    //!< First voltage
                       float voltage2,                    //!< Second voltage
                       float *LTC2654_lsb,                //!< Returns resulting LSB (volts)
                       int16_t *LTC2654_offset            //!< Returns resulting Offset (volts)
                      );
#endif  // LTC2654_H