Revision as of 08:05, 7 October 2011

Description

This 2 channels 10bits SPI DAC (Digital to Analog Converter) is mounted 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 3 of J5 on the APF51Dev). It's the 2nd output.

The default output voltage range is [0-2.5V] on the APF51Dev (because the 2,5V reference output of the AS1531 is used as reference input for the MCP4912).

Driver

The driver is included in the 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

Load driver

To use the DAC first load module:

# modprobe mcp49x2

Set channel 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 channel value to 2.48V (max range) :

# echo 1023 > out0_raw

To set the DAC B channel value to 1V :

# echo 412 > out1_raw

Links

• mcp4912 Datasheet
• DAC on Wikipedia