View source for PIC32MX: PWM Motor Control

Pulse Width Modulation, or PWM, is a technique used to vary the ''average'' magnitude of a signal by changing its '''duty cycle''' (the proportion of time that a signal is active or "high").  For a more in-depth introduction to PWM motor control click [[Pulse Width Modulation|here]].

PWM for PIC32 is discussed in more detail in the [http://ww1.microchip.com/downloads/en/DeviceDoc/61111D.pdf Microchip Output Compare documention]. 

==Available Pins==

The pins available for PWM are 5 input pins (OC1, OC2, OC3, OC4, and OC5) and 2 output pins (OCFA and OCFB). The output pins are for fault pin protection. 

==General Approach==
PWM can be set up by either changing the directly altering register bits or using the functions in outcompare.h (a header file included in the peripheral library (plib.h). The latter case is more straightforward and easier. This wiki describes how to use the outcompare functions. The register bits approach is described in detail in the[http://ww1.microchip.com/downloads/en/DeviceDoc/61111D.pdf Microchip Output Compare documention].

There are three main functions that are used for PWM. 

   void OpenOCX( config, value1, value2)
   void OpenTimerX(config, period)
   unsigned int SetDCOCXPWM(dutycycle)


where X is the module (1-5) or timer(2-3) that you want to use. Each of these functions are described below.

OpenOCX configures the OCX module and loads the R(value2) and RS (value1) registers with default values. An example is shown below:
   OpenOC1( OC_ON | OC_TIMER2_SRC | OC_PWM_FAULT_PIN_DISABLE, 0, 0);
The different configuration constants are shown below. If not specified, the default configuration is used. These constants are mutually exclusive for each category (ie you can only use one of them).
{| border="1" 
! style="background:#efefef;" | Config Constant !! style="background:#efefef;" | Description
|-
| OC_ON || Turns the Module ON
|-
| OC_OFF || Default - Turns the Module Off
|-
| colspan="2" align="center" style="background:#efefef;" | Stop-in-idle control
|-
| OC_IDLE_STOP || stop in idle mode
|-
| OC_IDLE_CON || Default - continue operation in idle mode
|-
| colspan="2" align="center" style="background:#efefef;" | 16/32 bit mode
|-
| OC_TIMER_MODE32 || Use 32 bit Mode
|-
| OC_TIMER_MODE16 || Default - Use 16 bit Mode
|-
| colspan="2" align="center" style="background:#efefef;" | Timer select
|-
| OC_TIMER3_SRC || Timer 3 is clock source
|-
| OC_TIMER2_SRC || Default - Timer 2 is clock source
|-
| colspan="2" align="center" style="background:#efefef;" | Operation mode select
|-
| OC_PWM_FAULT_PIN_ENABLE  || PWM Mode on OCx, fault pin enabled 
|-
| OC_PWM_FAULT_PIN_DISABLE || PWM Mode on OCx, fault pin disabled 
|-
| OC_CONTINUE_PULSE || Generates Continuous Output pulse on OCx Pin 
|- 
| OC_SINGLE_PULSE || Generates Single Output pulse on OCx Pin
|- 
| OC_TOGGLE_PULSE || Compare toggles OCx pin
|-
| OC_HIGH_LOW || Compare1 forces OCx pin Low
|-
| OC_LOW_HIGH || Compare1 forces OCx pin High
|-
| OC_MODE_OFF || Default - OutputCompare x Off
|}

For the operation mode, to use PWM one of the first two constants must be used.

The output compare modules use either Timer 2 (default) or Timer 3. These must be set up using OpenTimerX function, where X is either 2 or 3. The period can be between 0 and 0xFFFF inclusive. The OC can be configured to use a 32 bit timer in which both Timer 2 and Timer 3 are used.  
An example is shown below: 
   OpenTimer2( T2_ON | T2_PS_1_1 | T2_SOURCE_INT, 0xFFFF);

The configuration constants are shown below for Timer 2. Replace the 2 with a 3 for Timer 3. 
{| border="1" 
! style="background:#efefef;" | Config Constant !! style="background:#efefef;" | Description
|-
| T2_ON || Turns the Timer ON
|-
| T2_OFF || Default - Turns the Timer Off
|-
| colspan="2" align="center" style="background:#efefef;" | Stop-in-idle control
|-
| T2_IDLE_STOP || stop in idle mode
|-
| T2_IDLE_CON || Default - continue operation in idle mode
|-
| colspan="2" align="center" style="background:#efefef;" | Timer gate control
|-
| T2_GATE_ON || Timer Gate accumulation mode ON
|-
| T2_GATE_OFF || Default - Timer Gate accumulation mode OFF
|-
| colspan="2" align="center" style="background:#efefef;" | Prescale values
|-
| T2_PS_1_256 || Prescaler 1:256 
|-
| T2_PS_1_64 || 1:64
|-
| T2_PS_1_32 || 1:32
|-
| T2_PS_1_16 || 1:16
|-
| T2_PS_1_8 || 1:8
|-
| T2_PS_1_4 || 1:4
|-
| T2_PS_1_2 || 1:2
|-
| T2_PS_1_1 || Default - 1:1
|-
| colspan="2" align="center" style="background:#efefef;" | 32-bit or 16-bit
|-
| T2_32BIT_MODE_ON  || Enable 32-bit mode
|-
| T2_32BIT_MODE_OFF || Default
|-
| colspan="2" align="center" style="background:#efefef;" | Sync external clock option
|-
| T2_SOURCE_EXT || External clock source
|- 
| T2_SOURCE_INT || Internal Clock source
|}

The duty cycle can be updated by using SetDCOCXPWM(dutycycle) where X is the module. The duty cycle gets updated on the next cycle.

==Unidirectional Motor Control==
This section will detail how to set up a simple program and circuit to control a motor using a PIC microcontroller and PWM. 

===Sample Code===