MCP4912

Description

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

Connections

On your APF51Dev there are 2 signals to use:

• 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, and has to be selected (done by default on APF51):

[  ] $ 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