Revision as of 14:51, 26 April 2011

Description

This 2 channels 10bits SPI DAC (Digital to Analog Converter) is mounted in standard on the APF21Dev development boards.

Connections

On your Devlight/DevFull there are 3 signals to use the Max5821:

• DAC_OUTA: corresponds to OUTA (pin 7) on Max5821. It's the first output.
• DAC_OUTB: corresponds to OUTB (pin 8) on Max5821. It's the 2nd output.
• DAC_REF: corresponds to REF (pin 6) on Max5821. It's the reference voltage (max value that will be achieved by outputs). This input should be connected to a voltage reference between 0 and 3,3V.

Driver

The driver is included in ARMadeus distribution, then to use it, select it :

[  ] $ make linux26-menuconfig

Device Drivers  --->
    <*> Staging drivers  --->
        <*> Industrial I/O support  --->
            <M> Microchip MCP4902, MCP4912, MCP4922 driver

Then compile the distribution :

[  ] $ make linux26;make

Use it

modprobe

To use the DAC first load module:

# modprobe mcp49x2

set values

# cd /sys/bus/spi/devices/spi0.1/
# ls
dac_power_mode_0  out0_raw          power             uevent
dac_power_mode_1  out1_raw          subsystem

To set the dac value :

# cat in5_input 
887

Links

• mcp4912 Datasheet
• DAC on Wikipedia