© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
User manual
Rev. 01 — 15 August 2005
256
Philips Semiconductors
UM10139
Volume 1
Chapter 16: PWM
A sample of how PWM values relate to waveform outputs is shown in
. PWM
output logic is shown in
that allows selection of either single or double edge
controlled PWM outputs via the muxes controlled by the PWMSELn bits. The match
register selections for various PWM outputs is shown in
. This implementation
supports up to N-1 single edge PWM outputs or (N-1)/2 double edge PWM outputs, where
N is the number of match registers that are implemented. PWM types can be mixed if
desired.
[1]
Identical to single edge mode in this case since Match 0 is the neighboring match register. Essentially,
PWM1 cannot be a double edged output.
[2]
It is generally not advantageous to use PWM channels 3 and 5 for double edge PWM outputs because it
would reduce the number of double edge PWM outputs that are possible. Using PWM 2, PWM4, and
PWM6 for double edge PWM outputs provides the most pairings.
16.2.1 Rules for single edge controlled PWM outputs
1. All single edge controlled PWM outputs go high at the beginning of a PWM cycle
unless their match value is equal to 0.
Fig 60. Sample PWM waveforms
Table 245: Set and reset inputs for PWM Flip-Flops
PWM Channel
Single Edge PWM (PWMSELn = 0)
Double Edge PWM (PWMSELn = 1)
Set by
Reset by
Set by
Reset by
1
Match 0
Match 1
Match 1
2
Match 0
Match 2
Match 1
Match 2
3
Match 0
Match 3
Match 3
4
Match 0
Match 4
Match 3
Match 4
5
Match 0
Match 5
Match 5
6
Match 0
Match 6
Match 5
Match 6
PWM2
PWM4
PWM5
The waveforms below show a single PWM cycle and demonstrate PWM outputs under the
following conditions:
The timer is configured for PWM mode.
Match 0 is configured to reset the timer/counter
when a match event occurs.
Control bits PWMSEL2 and PWMSEL4 are set.
The match register values are as follows:
MRO = 100 (PWM rate)
MR1 = 41, MR2 = 78 (PWM2 output)
MR3 = 53, MR4 = 27 (PWM4 output)
MR5 = 65 (PWM5 output)
100
(counter is reset)
0
27
41
53
65
78