====== MCP4725 ======

The MCP4725 is a 12 bit digital to analog converter and can be powered from 2.7
to 5.5 volts. Datasheet [[https://cdn-shop.adafruit.com/datasheets/mcp4725.pdf|link]].

It is very simple to use. It has a 7 bit addressing scheme with a 3 bits that are
variable and called A0, A1 and A2. A2 and A1 are chosen at the order process and are
selected by selecting part numbers. A0 is broken out to a pin and is to be tied
either to GND or to VDD. On the adafruit board it is pulled low and also broken out. 

The ID of the standard chip with A0 pulled low. is ''%%0x62%%''. ''%%0x62%%'' is the first 7 bits of
the first byte we send out, which comes out to ''%%0b1100010%%''. When we tack on the R/W bit
as the LSBit this comes to:

<code>
0b11000100 or 0xC4 for Write
0b11000101 or 0xC5 for Read
</code>

Writes to set the output of this chip are done as a 12bit values which range from
''%%0x000%%'' which is ''%%0%%'' to ''%%0xFFF%%'' which is VDD - 1LSB. 

This chip has a bunch of fancy features such as power down modes for low power and
EEPROM to store output values. We don't need to use any of this stuff and just want
to use the fast mode and 0 for the power down vales. This makes the chip behave just
as we want it, output an analog signal when we tell it to!

To do this, write the following:

<code>
0xC4, 0x0P 0xQR 
</code>

PQR are is the hex value from ''%%0x000%%'' to ''%%0xFFF%%'' of the analog output we want.

To do this in the bust pirate, just set the thing up in [[I2C]], turn on the 5 volt rail
(its OK to do this, the device will talk to the chip just fine) and send out the
following:

<code>
[0xC4 0x0P 0xQR]
</code>

with PQR the number we want to send out.