mcp48x2_dac.c File Reference

Driver for the MCP4812 10 bit DAC (digital to analog converter) chip. More...

#include <util/delay.h>
#include <avr/interrupt.h>
#include "mcp48x2_dac.h"
#include "atmega_spi.h"
#include "pin_defines.h"

Go to the source code of this file.

Macros
#define	CHANNEL_BIT   15U
#define	GAIN_BIT   13U
#define	SHUTDOWN_BIT   12U
#define	TWELVE_BIT_LEVEL_OFFSET   0U
#define	TEN_BIT_LEVEL_OFFSET   2U
#define	EIGHT_BIT_LEVEL_OFFSET   4U
#define	TWELVE_BIT_MV_OFFSET   0U
#define	TEN_BIT_MV_OFFSET   1U
#define	EIGHT_BIT_MV_OFFSET   3U

Functions
void	chip_select (void)
	Private helper function - pulls CS line (Chip Select) low in order to begin SPI communication with DAC. More...
void	chip_deselect (void)
	Private helper function - pulls CS line (Chip Select) high to signal the end of SPI communication with DAC. More...
void	init_dac (dac_config_t *p_config)
	Initialisation routine (run once at startup). More...
void	dac_set_voltage (bool channel_a, uint16_t millivolts)
	Sends a new millivolts value to be output on DAC (Along with config settings). More...
void	dac_set_voltage_12_bit (bool channel_a, uint16_t millivolts, bool fractional)
	Sends a new millivolts value to be output on DAC (Along with config settings). More...
void	dac_reconfigure (void)
	Applies new config settings. More...
void	pulse_latch (void)
	Pulses LDAC pin low for a brief time (1uS). More...

Detailed Description

Driver for the MCP4812 10 bit DAC (digital to analog converter) chip.

Copyright

Copyright © 2022 by Jason Duffy.

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Author

Jason Duffy

Date

4th March 2022

This file provides the basic low-level functionality for the MCP4812 10 bit DAC from Microchip. This driver currently only allows for a single DAC to be used, but this might be improved on at a later date. This driver was written using the datasheet for the Microchip MCP4812 chip, which can be found at the link below.

See also

https://ww1.microchip.com/downloads/en/DeviceDoc/20002249B.pdf

Definition in file mcp48x2_dac.c.

Macro Definition Documentation

CHANNEL_BIT

#define CHANNEL_BIT   15U

Definition at line 46 of file mcp48x2_dac.c.

GAIN_BIT

#define GAIN_BIT   13U

Definition at line 47 of file mcp48x2_dac.c.

SHUTDOWN_BIT

#define SHUTDOWN_BIT   12U

Definition at line 48 of file mcp48x2_dac.c.

TWELVE_BIT_LEVEL_OFFSET

#define TWELVE_BIT_LEVEL_OFFSET   0U

Definition at line 51 of file mcp48x2_dac.c.

TEN_BIT_LEVEL_OFFSET

#define TEN_BIT_LEVEL_OFFSET   2U

Definition at line 52 of file mcp48x2_dac.c.

EIGHT_BIT_LEVEL_OFFSET

#define EIGHT_BIT_LEVEL_OFFSET   4U

Definition at line 53 of file mcp48x2_dac.c.

TWELVE_BIT_MV_OFFSET

#define TWELVE_BIT_MV_OFFSET   0U

Definition at line 56 of file mcp48x2_dac.c.

TEN_BIT_MV_OFFSET

#define TEN_BIT_MV_OFFSET   1U

Definition at line 57 of file mcp48x2_dac.c.

EIGHT_BIT_MV_OFFSET

#define EIGHT_BIT_MV_OFFSET   3U

Definition at line 58 of file mcp48x2_dac.c.

Function Documentation

chip_select()

void chip_select

(

void

)

Private helper function - pulls CS line (Chip Select) low in order to begin SPI communication with DAC.

Definition at line 302 of file mcp48x2_dac.c.

{
    DAC_CTRL_PORT &= ~(1 << DAC_CS);
}

chip_deselect()

void chip_deselect

(

void

)

Private helper function - pulls CS line (Chip Select) high to signal the end of SPI communication with DAC.

Definition at line 311 of file mcp48x2_dac.c.

{
    DAC_CTRL_PORT |= (1 << DAC_CS);
}

init_dac()

void init_dac

(

dac_config_t *

p_config

)

Initialisation routine (run once at startup).

This function is to be called before using any other DAC functions. Instantiate the dac_config_t object first then pass it's address into and call init_lcd() before using any other lcd functions.

Parameters

p_config

is a pointer to the dac_config_t object.

Definition at line 89 of file mcp48x2_dac.c.

{
    // Copy config object pointer to a variable with file scope. 
    p_config_global = p_config;
 
    // Delay to allow power ramp up in device.
    _delay_ms(500);
 
    // Initialise SPI comms. 
    init_spi(lsb_first,
             controller,
             rising_edge,
             sample_leading_edge,
             cpu_clk_div_16,
             single_speed);
 
    DAC_CTRL_DDR |= (1 << DAC_CS); // Set chip select as output.
    DAC_CTRL_PORT |= (1 << DAC_CS); // Set CS line high (not selected).
    DAC_CTRL_DDR |= (1 << LDAC); // Set LDAC line (latch) as output.
    DAC_CTRL_PORT |= (1 << LDAC); // Set LDAC high.
 
    // Save the value to bitshift millivolts value by. 
    if (p_config_global->model == mcp4802)
    {
      mv_resolution_shift = EIGHT_BIT_MV_OFFSET;
      level_resolution_shift = EIGHT_BIT_LEVEL_OFFSET;
    }
    else if (p_config_global->model == mcp4812)
    {
      mv_resolution_shift = TEN_BIT_MV_OFFSET;
      level_resolution_shift = TEN_BIT_LEVEL_OFFSET;
    }
    else
    {
      mv_resolution_shift = TWELVE_BIT_MV_OFFSET;
      level_resolution_shift = TWELVE_BIT_LEVEL_OFFSET;
    }  
 
    // Establish latching settings
    if (!p_config_global->sync_manually)
    {
      DAC_CTRL_PORT &= ~(1 << LDAC);
    }
 
    // Send new values to DAC
    dac_reconfigure();
}

dac_set_voltage()

void dac_set_voltage	(	bool	channel_a,
		uint16_t	millivolts
	)

Sends a new millivolts value to be output on DAC (Along with config settings).

For 8 or 10 bit models only.

Parameters

channel_a	true = Channel A, false = Channel B.
millivolts	mV value to be output by DAC. Ensure that this value doesn't exceed the maxixum for the DAC model and gain setting.

Definition at line 145 of file mcp48x2_dac.c.

{
    // Manipulate mv value to suit register size of chip and gain setting.
    if (channel_a)
    {
        if (p_config_global->channel_a.gain_low)
        {   
            p_config_global->channel_a.level =
                                (millivolts >> mv_resolution_shift);
        }
        else
        {
            p_config_global->channel_a.level =
                                (millivolts >> (mv_resolution_shift + 1));
        }
    }
    else
    {
        if (p_config_global->channel_b.gain_low)
        {
            p_config_global->channel_b.level =
                                (millivolts >> mv_resolution_shift);
        }
        else
        {
            p_config_global->channel_b.level =
                                (millivolts >> (mv_resolution_shift + 1));
        }
    }
 
    // Send new values to DAC
    dac_reconfigure();
}

dac_set_voltage_12_bit()

void dac_set_voltage_12_bit	(	bool	channel_a,
		uint16_t	millivolts,
		bool	fractional
	)

Sends a new millivolts value to be output on DAC (Along with config settings).

For 12 bit models only.

Parameters

channel_a	true = Channel A, false = Channel B.
millivolts	mV value to be output by DAC. Ensure that this value doesn't exceed the maxixum for the DAC model and gain setting.
fractional	true = millivolts value has 0.5mV added to it. Only to be used when gain_low is true.

Definition at line 189 of file mcp48x2_dac.c.

{
    if (channel_a)
    {
        if(p_config_global->channel_a.gain_low)
        {
            p_config_global->channel_a.level =
                                (millivolts << (TWELVE_BIT_MV_OFFSET + 1));
            // Add the 0.5mV value if required. 
            if (fractional == true)
            {
                p_config_global->channel_a.level += 1;
            }
        }
        else
        {
            p_config_global->channel_a.level =
                                (millivolts << TWELVE_BIT_MV_OFFSET);
        }
    }
    else
    {
        if(p_config_global->channel_b.gain_low)
        {
            p_config_global->channel_b.level =
                                (millivolts << (TWELVE_BIT_MV_OFFSET + 1));
            // Add the 0.5mV value if required. 
            if (fractional == true)
            {
                p_config_global->channel_b.level += 1;
            }
        }
        else
        {
            p_config_global->channel_b.level =
                                (millivolts << TWELVE_BIT_MV_OFFSET);
        }
    }
 
    // Send new values to DAC
    dac_reconfigure();
}

dac_reconfigure()

void dac_reconfigure

(

void

)

Applies new config settings.

This function takes updated config settings for both channels of DAC, then re-sends data so that the new settings take effect.

Definition at line 240 of file mcp48x2_dac.c.

{
    uint16_t channel_a_data = 0;
    uint16_t channel_b_data = 0;
 
    // Set up config bits in 16bit word to be sent. 
    channel_a_data &= ~(1 << CHANNEL_BIT); // Clear channel bit (Channel A).
    channel_a_data |= (p_config_global->channel_a.gain_low << GAIN_BIT);
    channel_a_data |= (p_config_global->channel_a.active << SHUTDOWN_BIT);
 
    channel_b_data |= (1 << CHANNEL_BIT); // Set channel bit (Channel B).
    channel_b_data |= (p_config_global->channel_b.gain_low << GAIN_BIT);
    channel_b_data |= (p_config_global->channel_b.active << SHUTDOWN_BIT);
 
    // Shift level into correct place for chip and OR it into our 16bit word.
    channel_a_data |=
                (p_config_global->channel_a.level << level_resolution_shift);
 
    channel_b_data |=
                (p_config_global->channel_b.level << level_resolution_shift);
                
 
    // Send data for channel A to DAC over SPI. 
    chip_select();
    spi_trade_word(channel_a_data);
    chip_deselect();
 
    // Send data for channel B to DAC over SPI.
    chip_select();
    spi_trade_word(channel_b_data);
    chip_deselect();
 
    // If sync_manually is set to false, pulse LDAC to update values. 
    if (!p_config_global->sync_manually)
    {
        pulse_latch();
    }
}

pulse_latch()

void pulse_latch

(

void

)

Pulses LDAC pin low for a brief time (1uS).

When sync_manually is true, call this function to latch both config settings and new voltage value into both channels of DAC simultaneously.

Definition at line 286 of file mcp48x2_dac.c.

{
    DAC_CTRL_PORT &= ~(1 << LDAC);
    _delay_us(1);
    DAC_CTRL_PORT |= (1 << LDAC);
}