PIC18F2331_07 Datasheet, PDF (194/400 Pages) Microchip Technology – 28/40/44-Pin Enhanced Flash Microcontrollers with nanoWatt Technology, High Performance PWM and A/D

PIC18F2331/2431/4331/4431
17.4.4 INTERRUPTS IN DOUBLE UPDATE
MODE
This mode is available in Continuous Up/Down Count
mode. In the Double Update mode (PTMOD<1:0> = 11),
an interrupt event is generated each time the PTMR
register is equal to zero and each time the PTMR
matches with PTPER register. Figure 17-8 shows the
interrupts in Continuous Up/Down Count mode with
double updates.
The Double Update mode provides two additional
functions to the user in Center-Aligned mode.
1. The control loop bandwidth is doubled because
the PWM duty cycles can be updated twice per
period.
2. Asymmetrical center-aligned PWM waveforms
can be generated, which are useful for
minimizing output waveform distortion in certain
motor control applications.
Note:
Do not change PTMOD while PTEN is
active. It will yield unexpected results. To
change the PWM Timer mode of opera-
tion, first clear PTEN bit, load PTMOD with
required data and then set PTEN.
FIGURE 17-8:
PWM TIME BASE INTERRUPT, CONTINUOUS UP/DOWN COUNT MODE WITH
DOUBLE UPDATES
A: PRESCALER = 1:1
Case 1: PTMR Counting Upwards
Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4
OSC1
PTMR
3FDh
3FEh
2
3FFh
3FEh
3FDh
PTDIR bit
PTMR_INT_REQ
1
1
1
1
PTIF bit
Case 2: PTMR Counting Downwards
Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4
OSC1
PTMR
PTDIR bit
PTMR_INT_REQ
1
PTIF bit
002h
001h
1
000h
001h
1
1
002h
Note 1: Interrupt flag bit, PTIF, is sampled here (every Q1).
2: PWM Time Base Period register, PTPER, is loaded with the value 3FFh for this example.
DS39616C-page 192
Preliminary
© 2007 Microchip Technology Inc.