PIC24FJ256GB108-I Datasheet, PDF (174/352 Pages) Microchip Technology – 64/80/100-Pin, 16-Bit Flash Microcontrollers with USB On-The-Go (OTG)

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14.2 Compare Operations
In Compare mode (Figure 14-1), the output compare
module can be configured for single-shot or continuous
pulse generation; it can also repeatedly toggle an
output pin on each timer event.
To set up the module for compare operations:
1. Configure the OCx output for one of the
available Peripheral Pin Select pins.
2. Calculate the required values for the OCxR and
(for Double Compare modes) OCxRS duty cycle
registers:
a) Determine the instruction clock cycle time.
Take into account the frequency of the
external clock to the timer source (if one is
used) and the timer prescaler settings.
b) Calculate time to the rising edge of the out-
put pulse relative to the timer start value
(0000h).
c) Calculate the time to the falling edge of the
pulse based on the desired pulse width and
the time to the rising edge of the pulse.
3. Write the rising edge value to OCxR, and the
falling edge value to OCxRS.
4. Set the Timer Period register, PRy, to a value
equal to or greater than the value in OCxRS.
5. Set the OCM<2:0> bits for the appropriate
compare operation (= 0xx).
6. For Trigger mode operations, set OCTRIG to
enable Trigger mode. Set or clear TRIGMODE to
configure trigger operation, and TRIGSTAT to
select a hardware or software trigger. For
Synchronous mode, clear OCTRIG.
7. Set the SYNCSEL<4:0> bits to configure the
trigger or synchronization source. If free-running
timer operation is required, set the SYNCSEL
bits to ‘00000’ (no sync/trigger source).
8. Select the time base source with the
OCTSEL<2:0> bits. If necessary, set the TON bit
for the selected timer which enables the compare
time base to count. Synchronous mode operation
starts as soon as the time base is enabled; Trigger
mode operation starts after a trigger source event
occurs.
FIGURE 14-1:
OUTPUT COMPARE BLOCK DIAGRAM (16-BIT MODE)
OCTSELx
SYNCSELx
TRIGSTAT
TRIGMODE
OCTRIG
OC Clock
Sources
Trigger and
Sync Sources
Clock
Select
Increment
Reset
Trigger and
Sync Logic
Match Event
Reset
OCxCON1
OCxCON2
OCxR
Comparator
Match Event
OCMx
OCINV
OCTRIS
FLTOUT
FLTTRIEN
FLTMD
ENFLT0
OCFLT0
OCxTMR
Comparator
Match Event
OC Output and
Fault Logic
OCxRS
OCx Interrupt
OCx Pin⁽¹⁾
OCFA/OCFB
Note 1: The OCx outputs must be assigned to an available RPn pin before use. Please see Section 10.4 “Peripheral
Pin Select” for more information.
DS39897C-page 174
 2009 Microchip Technology Inc.