AD56X8

Experimental Library for the AD56X8 series digital analog convertor.

Note: not yet tested with hardware, TODO buy hardware.

Feedback, issues, improvements are welcome. Please file an issue on GitHub.

Description

The AD56X8 is an 8 channel DAC convertor, that has 12, 14 or 16 bit accuracy. Furthermore it is available in 2.5 V and 5.0 V version, see table below.

The device allows to set the outputs directly, or prepare them and update them simultaneously (Latch DAC).

type	output	resolution	power up
AD5668-1	2.5 V	16 bit	0.0 V
AD5648-1	2.5 V	14 bit	0.0 V
AD5628-1	2.5 V	12 bit	0.0 V
AD5668-3	5.0 V	16 bit	2.5 V
AD5668-2	5.0 V	16 bit	0.0 V
AD5648-2	5.0 V	14 bit	0.0 V
AD5628-2	5.0 V	12 bit	0.0 V

The library is usable but not functional complete yet. At least it lacks support for:

• RESET pin,
• VREF pin.
• other points mentioned in future section below.

0.3.0 Breaking change

Version 0.3.0 introduced a breaking change to improve handling the SPI dependency. The user has to call SPI.begin() or equivalent before calling AD.begin(). Optionally the user can provide parameters to the SPI.begin(...)

0.2.0 breaking change

The version 0.2.0 has breaking changes in the interface. The essence is removal of ESP32 specific code from the library. This makes it possible to support the ESP32-S3 and other processors in the future. Also it makes the library a bit simpler to maintain.

Note the order of the parameters of the software SPI constructor has changed in 0.2.0.

Related

This library is partly inspired by https://github.com/bobhart/AD5668-Library, kudo's to Bob! Discussed here - https://forum.arduino.cc/t/new-library-for-the-ad5668-dac/340393

Some differences between this library and Bob Harts. This library

• caches the values of all channels, so they can be read back.

• has derived classes for every specific type DAC. This allows value range checking.

• caches the LDAC mask, so it can be read back and updated.

• allows to set SPI-speed.

• has faster software SPI transfer, on ESP32 this rivals HW SPI.

• MIT license instead of GNU v3

• https://github.com/RobTillaart/AD568X (single channel 12, 14, 16 bit)

• https://github.com/RobTillaart/AD5680 (single channel 18 bit)

• https://github.com/RobTillaart/MCP_DAC (SPI interface)

Interface

#include "AD56X8.h"

Base class

Should not be used to instantiate a device as the derived types have correct number of bits.

• AD56X8(uint8_t slaveSelect, SPIClassRP2040 * mySPI = &SPI) constructor HW SPI (RP2040 specific). Sets internal value to zero.
• AD56X8(uint8_t slaveSelect, SPIClass * mySPI = &SPI) constructor HW SPI. Sets internal value to zero.
• AD56X8(uint8_t spiData, uint8_t spiClock, uint8_t slaveSelect) constructor, sets SW SPI. Sets internal values to zero.
• void begin() initializes the SPI and sets internal state.
• uint8_t getType() returns bit depth (see below).

Derived classes (preferred use)

The parameters for the specific constructors are identical to the base class. One should use these, as these set the bit resolution!

• AD5628(uint8_t slaveSelect, ..) constructor, 16 bit. Starts up at midscale = 32768.
• AD5648(uint8_t slaveSelect, ..) constructor, 14 bit.
• AD5668(uint8_t slaveSelect, ..) constructor, 16 bit.
• AD5668_3(uint8_t slaveSelect, ..) constructor, 16 bit.

Set DAC

• bool setValue(uint8_t channel, uint16_t value) set value to the output immediately, effectively a prepare + update in one call. Returns false if channel out of range.
• uint16_t getValue(uint8_t channel) returns set OR prepared value. At power up the DAC's will be reset to 0 V except the AD5668-3 (2.5V).
• bool setPercentage(uint8_t channel, float percentage) sets the output as a percentage 0..100. If percentage is out of range, it is not set and the function returns false.
• float getPercentage(uint8_t channel) returns percentage, wrapper around getValue(). Might return a slightly different value than setPercentage() due to rounding errors.
• bool prepareChannel(uint8_t channel, uint16_t value) prepares the value for a channel. Returns false if channel out of range.
• bool updateChannel(uint8_t channel) writes the prepared value to ADC. Returns false if channel out of range.
• void updateAllChannels() writes all prepared channels to their ADC simultaneously by applying a SW latch pulse (LDAC).

Note: the valid range of value is not checked by the library.

LDAC

The AD56X8 has an LDAC register with one bit per channel. This is to configure which channels are updated simultaneously. Read datasheet for details.

• void setLDACmask(uint8_t mask = 0x00) sets 8 channels with one call by using a bit mask. Default value 0x00 clears all channels.
• uint8_t getLDACmask() return the current (cached) LDAC bit mask, default = 0x00.
• bool inLDACmask(uint8_t channel) returns true if a channel is in the current LDAC bit mask. Returns also false if channel is out of range.

LDAC (hardware pin)

The use of the LDAC interface is optional. It allows a prepared value to be set in in the DAC register. See prepareValue(). If you control multiple devices the hardware LDAC allows you to set a new value on all devices simultaneously.

• void setLDACPin(uint8_t ldac) set the LDAC pin.
• void triggerLDAC() give a pulse over the LDAC line.

Powermode

• bool setPowerMode(uint8_t powerDownMode, uint8_t mask = 0x00) powerDownMode = 0..3. Default is setting the channels to PWR_NORMAL. Returns false if powerDownMode is out of range.

mode	define
0x00	AD56X8_PWR_NORMAL
0x01	AD56X8_PWR_1K
0x02	AD56X8_PWR_100K
0x03	AD56X8_PWR_TRI

Misc

• void reset() software reset.
• bool setClearCode(uint8_t CCmode) Set the startup value. CCmode = 0..3, see table below. Returns false if mode out of range.

mode	define	notes
0x00	AD56X8_CC_0000
0x01	AD56X8_CC_8000
0x02	AD56X8_CC_FFFF
0x03	AD56X8_CC_NOP	do not use => Read datasheet.

SPI

• void setSPIspeed(uint32_t speed) sets SPI clock in Hz, please read datasheet of the ADC first to get optimal speed.
• uint32_t getSPIspeed() gets current speed in Hz.
• bool usesHWSPI() returns true if HW SPI is used.

SPI ESP32 specific

Note: earlier experiments shows that on a ESP32 SW-SPI is equally fast as HW-SPI and in fact a bit more stable. The SW pulses are a bit slower than the HW pulses and therefore more square. The HW-SPI has some overhead SW-SPI hasn't.

Operation

The examples (should) show the basic working of the functions. Note that the library is not tested with hardware yet. (based upon datasheet)

Future

Must

• update and improve documentation
• get test hardware
• test the library
• write unit test
• check TODO in code
• keep in sync with AD5680 + AD568X library

Should

• write examples
  • LDAC
  • power mode
• support for RESET pin
  • void setResetPin(uint8_t pin)
  • void triggerReset()
• support for EXTERNAL VREF
  • how?

Could

• CCmode + reset implies start value for getValue(ch)
  • is this implementable? costs?

Wont

• investigate value range checking for AD5648 and AD5628
  • now setValue() returns false if value > max,
  • should value be clipped instead?
  • setPercentage() idem.
  • user responsibility

Support

If you appreciate my libraries, you can support the development and maintenance. Improve the quality of the libraries by providing issues and Pull Requests, or donate through PayPal or GitHub sponsors.

Thank you,