The AD5781 is a single 18-bit, unbuffered voltage-output DAC that operates from a bipolar supply of up to 33 V. The AD5781 accepts a positive reference input in the range 5V to VDD – 2.5 V and a negative reference input in the range VSS + 2.5 V to 0 V. The AD5781 offers a relative accuracy specification of ±0.5 LSB max, and operation is guaranteed monotonic with a ±0.5 LSB DNL max specification.
The part uses a versatile 3-wire serial interface that operates at clock rates up to 35 MHz and that is compatible with standard SPI®, QSPI™, MICROWIRE™, and DSP interface standards. The part incorporates a power-on reset circuit that ensures the DAC output powers up to 0 V and in a known output impedance state and remains in this state until a valid write to the device takes place. The part provides an output clamp feature that places the output in a defined load state.
The goal of this project (Microcontroller No-OS) is to be able to provide reference projects for lower end processors, which can't run Linux, or aren't running a specific operating system, to help those customers using microcontrollers with ADI parts. Here you can find a generic driver which can be used as a base for any microcontroller platform and also specific drivers for different microcontroller platforms.
The driver contains two parts:
The Communication Driver has a standard interface, so the AD5781 driver can be used exactly as it is provided.
There are three functions which are called by the AD5781 driver:
SPI driver architecture
The following functions are implemented in this version of AD5781 driver:
|long AD5781_Init(void)||Initializes the communication with the device. Return 0 in case of success and negative error code otherwise.|
|long AD5781_SetRegisterValue(unsigned char registerAddress, unsigned long registerValue)||Writes data into a register. Receives as parameters the address of the register and the value of the register. Returns 0 in case of success or negative error code.|
|long AD5781_GetRegisterValue(unsigned char registerAddress)||Reads the value of a register. Receives as parameter the address of the register. Returns the value of the register or negative error code.|
|long AD5781_DacOuputState(unsigned char state)||Sets the DAC output in one of the three states(normal, clamped via 6KOhm to GND, tristate). Returns negative error code or 0 in case of success.|
|long AD5781_SetDacValue(unsigned long value)||Writes to the DAC register. Receives as parameter the value to be written to DAC. Returns negative error code or 0 in case of success.|
|long AD5781_SoftInstruction(unsigned char instructionBit)||Asserts RESET, CLR or LDAC in a software manner. Receives as parameter one of the software control bits(RESET, CLR or LDAC). Returns negative error code or 0 in case of success.|
|long AD5781_Setup(unsigned long setupWord)||Configures the output amplifier, DAC coding, SDO state and the linearity error compensation. Receives as parameter a 24-bit value that sets or clears the Control Register bits(RBUF, BIN/2sC, SDODIS, LINCOMP). Returns negative error code or 0 in case of success.|
This section contains a description of the steps required to run the AD7303 demonstration project on a Digilent Cerebot MX3cK platform.
The AD5781 demonstration project for PIC32MX320F128H consists of three parts: the AD5781 Driver, the PmodDA5 Demo for PIC32MX320F128H and the PIC32MX320F128H Common Drivers.
All three parts have to be downloaded.
The following commands were implemented in this version of AD5781 reference project for Cerebot MX3cK board.
|help?||Displays all available commands.|
|reset!||Resets the AD5781 device.|
|coding=|| Selects the coding style. Accepted values:
0 - Offset binary coding.
1 - Two's complement coding.(default)
|coding?||Display the current coding style.|
|register=|| Writes to the DAC register. Accepted values:
0 .. 262143 - the value written to the DAC.
|register?||Displays last written value to the DAC register.|
|voltage=|| Sets the DAC output voltage. Accepted values:
-10 .. +10 - desired output voltage in volts.
|voltage?||Displays the output voltage.|
|output=|| Selects the DAC output state. Accepted values:
0 - Normal state.
1 - Clamped via 6KOhm to AGND.
2 - Tristate.(default)
|output?||Displays the DAC output state.|
|rbuf=|| Sets/resets the RBUF bit from control register. Accepted values:
0 - RBUF is reset.
1 - RBUF is set.(default)
|rbuf?||Displays the value of RBUF bit from control register.|
Commands can be executed using a serial terminal connected to the UART1 peripheral of PIC32MX320F128H.
The following image shows a generic list of commands in a serial terminal connected to processor’s UART peripheral.
This section presents the steps for developing a software application that will run on the Digilent Cerebot MX3cK development board for controlling and monitoring the operation of the ADI part.