MCP4912

Description

This 2 channels 10bits SPI DAC (Digital to Analog Converter) is mounted in standard on the APF51Dev development boards.

Connections

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

• DAC_OUTA: corresponds to OUTA (pin 1 of J5 on the APF51Dev). It's the first output.
• DAC_OUTB: corresponds to OUTB (pin 10 of J5 on the APF51Dev). It's the 2nd output.

The default output voltage range is 0->2.5V on the APF51Dev because the reference output of the AS1531 is used as reference for the mcp4912

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/device0
# ls
dac_power_mode_0  out0_raw          power             uevent
dac_power_mode_1  out1_raw          subsystem

To set the dac A value to 2.48V (max range) :

# echo 1023 > out0_raw

To set the dac B value to 1V :

# echo 412 > out1_raw

Links

• mcp4912 Datasheet
• DAC on Wikipedia