Compare mode of CCP
Compare Mode Block Diagram
Explanation of Compare Mode Block Diagram
In Compare mode, the 16-bit CCPRx register value is constantly compared against either the TMR1 or TMR3 register pair value.
When a match occurs, the CCPx pin can be:
- driven high
- driven low
- toggled (high-to-low or low-to-high)
- remain unchanged (that is, reflects the state of the I/O latch)
The action on the pin is based on the value of the mode select bits (CCPxM<3:0>). At the same time, the interrupt flag bit, CCPxIF, is set.
CCP PIN CONFIGURATION
The user must configure the CCPx pin as an output by clearing the appropriate TRIS bit.
TIMER1/TIMER3 MODE SELECTION
Timer1 and/or Timer3 must be running in Timer mode or Synchronized Counter mode if the CCP module is using the compare feature. In Asynchronous Counter mode, the compare operation may not work.
SOFTWARE INTERRUPT MODE
When the Generate Software Interrupt mode is chosen (CCPxM<3:0> = 1010), the corresponding CCPx pin is not affected. A CCP interrupt is generated when the CCPxIF interrupt flag is set while the CCPxIE bit is set.
SPECIAL EVENT TRIGGER
Both CCP modules are equipped with a Special Event Trigger. This is an internal hardware signal generated in Compare mode to trigger actions by other modules. The Special Event Trigger is enabled by selecting the Compare Special Event Trigger mode (CCPxM<3:0> = 1011). For either CCP module, the Special Event Trigger resets the Timer register pair for whichever timer resource is currently assigned as the module’s time base. This allows the CCPRx registers to serve as a programmable Period register for either timer. The Special Event Trigger for CCP2 can also start an A/D conversion. In order to do this, the A/D Converter must already be enabled.