View source for NU32: Using the dsPIC33FJ12MC201 QEI to SPI board

Using the dsPIC33FJ12MC201 breakout board for quadrature decoding.

[[Image:NU32_dsPIC33FJ12MC201.jpg|thumb|200px|The dsPIC33FJ12MC201 breakout board|center]]

== Overview ==

[[Media:dsPIC33FJ12MC201.pdf|Datasheet]]

The dsPIC series of PIC microcontrollers are inexpensive 16 bit microcontrollers, specializing in the ability do fast digital signal processing.

The dsPIC33FJ12MC201 is a low pin count chip that runs on 3.3V at 80MHz without an external oscillator. It has the ability to remap peripheral functionality to any pins (labeled RPx). It also has a special peripheral called QEI, or Quadrature Encoder Interface. The QEI module receives the quadrature square waves from an encoder and keeps track of the net motion of the encoder as a 16 bit unsigned integer.

== Details ==
The breakout board has been pre-programmed to read a quadrature signal on pins RP7 and RP8 (pins 11 and 12). It will keep track of the net motion of the encoder as a 16 bit integer, initializing to 32767. The dsPIC will report the 16 bit unsigned number over SPI communication when a '1' is sent.

[[Image:NU32_dsPIC33FJ12MC201_sch.png|thumb|400px|The dsPIC33FJ12MC201 breakout board schematic|center]]

== Wiring ==

[[Image:NU32_dsPIC33FJ12MC201_wire.jpg|thumb|200px|How to connect the dsPIC33FJ12MC201 breakout board to the PIC32|center]]

== Library Functions ==
[[Media:NU32_dsPIC_QEU_example.c | This code]] is an example of how to read the encoder count using the NU32.

The functions are:
*void initEncoderSPI(void) - enables SPI4 as master at 8MHz
*int getEncoder(void) - sends a '1' to the dsPIC, returns the value returned by the dsPIC

NU32_dsPIC_Example.c above demonstrates how to use the breakout board.

== Sample Code ==

To initialize the SPI communication, call initEncoderSPI(), :

<pre>
  initEncoderSPI();
</pre>

To read the encoder count, call getEncoder(), :

<pre>
  int count = getEncoder();
</pre>

== More Information ==
The internal count of the encoder will "roll over" at 0 or 65535. It is up to you to note that if the encoder count has made an unreasonable change, it has probably rolled over!