Datasheet

PIC18F2331/2431/4331/4431
DS39616D-page 182  2010 Microchip Technology Inc.
18.4.2 INTERRUPTS IN SINGLE-SHOT
MODE
When the PWM time base is in the Single-Shot mode
(PTMOD<1:0> = 01), an interrupt event is generated
when a match with the PTPER register occurs. The
PWM Time Base register (PTMR) is reset to zero on
the following input clock edge and the PTEN bit is
cleared. The postscaler selection bits have no effect in
this Timer mode.
18.4.3 INTERRUPTS IN CONTINUOUS
UP/DOWN COUNT MODE
In the Continuous Up/Down Count mode
(PTMOD<1:0> = 10), an interrupt event is generated
each time the value of the PTMR register becomes
zero and the PWM time base begins to count upwards.
The postscaler selection bits may be used in this mode
of the timer to reduce the frequency of the interrupt
events. Figure 18-7 shows the interrupts in Continuous
Up/Down Count mode.
FIGURE 18-6: PWM TIME BASE INTERRUPT TIMING, SINGLE-SHOT MODE
Q2Q1 Q3 Q4Q2Q1 Q3 Q4 Q2Q1 Q3 Q4 Q2Q1 Q3 Q4 Q2Q1 Q3 Q4
1
1
F
OSC/4
PTMR
FFEh FFFh 000h 000h 000h
1
PTIF bit
2
Note 1: Interrupt flag bit, PTIF, is sampled here (every Q1).
2: PWM Time Base Period register, PTPER, is loaded with the value, FFFh, for this example.
QcQc Qc QcQcQc Qc Qc QcQc Qc Qc QcQc Qc Qc QcQc Qc Qc
1
1
PTMR
FFEh FFFh
000h 000h
1
2
A: PRESCALER = 1:1
B: PRESCALER = 1:4
PTMR_INT_REQ
Q4Q4
PTIF bit
PTMR_INT_REQ
000h