MAX5842

Quad, 12-Bit, Low-Power, 2-Wire, Serial Voltage-Output DAC

• Maxim Homepage
• Datasheet

Development Log

Chris did some Ninja soldering:

Looked up details in the the datasheet:

• Interface is I2C compatible, up to 400KHz
• 2.7-5.5v

So all looks fine for normal connection to mbed

      +--------+
 ADD -| 1   10 |- OUTD
 SCL -| 2    9 |- OUTC
 VDD -| 3    8 |- OUTB
 GND -| 4    7 |- OUTA
 SDA -| 5    6 |- REF
      +--------+
    MAX5842 Pinout

Non-obvious pins and things picked out of description:

• ADD - sets the address LSB (will set to 0v)
• REF - the voltage the output is a proportion of (will set to 3.3v)
• VOUT = (VREF * value)/4095
• Following power-up, a wake-up command must be initiated before any conversions are performed
• The MAX5842 SDA and SCL drivers are open-drain outputs, requiring a pullup resistor to generate a logic high voltage

Addresses:

         +-------------------+
MAX5842L | 011110 | ADD | RW |
MAX5842M | 101110 | ADD | RW |
         +-------------------+

Text is very small, but I think I've got an L.

For writes, bits C3-C0 configure and bits D11-D0 are DAC data. Also an extended set for controlling power

+--------------+ +--------------+
| C3-0 | D11-8 | |    D7-0      |
+--------------+ +--------------+

+--------------+ +-----------------+
| 1111 | 0000  | | xx DCBA PD1 PD0 |
+--------------+ +-----------------+

Write a simple sanity program to dump out the value of an AnalogIn pin, which is connected to the output A of the MAX part.

#include "mbed.h"

AnalogIn res(p16);
DigitalOut myled(LED1);

int main() {
    while(1) {
        printf("res = %f\n", res.read());
        myled = !myled;
        wait(0.25);
    }
}

works :)

Ok, lets try wiring and write something...

Schematic

  ---+--+--- 3.3v
     |  |                                       |
     #  #                                       # pull-up resistors for I2C
     #  #        +--------+                     # I used ~1k, just because that is what was around
0v --|--|-- ADD -| 1   10 |- OUTD               |
p10 -o--|-- SCL -| 2    9 |- OUTC
3.3v ---|-- VDD -| 3    8 |- OUTB
0v -----|-- GND -| 4    7 |- OUTA ---- p16
p9 -----o-- SDA -| 5    6 |- REF ----- 3.3v
                 +--------+

#include "mbed.h"

AnalogIn res(p16);
DigitalOut myled(LED1);

I2C max5842(p9, p10);

int main() {

    // ADDR: 011 110 ADD, ADD = 0 
    // 011 1100 == 0x3C
    int addr = 0x3C;

    char data[2] = {0x08, 0xF0};
    max5842.write(addr, data, 2);

    while(1) {
        printf("res = %f\n", res.read());
        myled = !myled;
        wait(0.25);
    }
}

No error, so know address is right, as if change it I2C fails.

AnalogIn is 0, so need to perhaps now do powerup sequence:

    // Power up the DAC
    // - Extended Commands [ 1111 0000 xx DCBA PD1 PD0 ]
    // - DCBA = 1111 means select all, PD = 00 means power on
    char power_up[2] = {0xF0, 0x3C};
    max5842.write(addr, power_up, 2);

Yep! It is alive!

Resulting test program:

• http://mbed.org/users/simon/published/be3740460f6f4c3d180fab2987f3190c/MAX5842.zip