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Philips Semiconductors
Volume 1
16.2.2 Rules for double edge controlled PWM outputs
Five rules are used to determine the next value of a PWM output when a new cycle is
about to begin:
16.3 Pin description
Table 246
Table 246: Pin summary
Pin
PWM1
PWM2
PWM3
PWM4
PWM5
PWM6
16.4 Register description
The PWM function adds new registers and registers bits as shown in
User manual
2. Each PWM output will go low when its match value is reached. If no match occurs (i.e.
the match value is greater than the PWM rate), the PWM output remains continuously
high.
1. The match values for the next PWM cycle are used at the end of a PWM cycle (a time
point which is coincident with the beginning of the next PWM cycle), except as noted
in rule 3.
2. A match value equal to 0 or the current PWM rate (the same as the Match channel 0
value) have the same effect, except as noted in rule 3. For example, a request for a
falling edge at the beginning of the PWM cycle has the same effect as a request for a
falling edge at the end of a PWM cycle.
3. When match values are changing, if one of the "old" match values is equal to the
PWM rate, it is used again once if the neither of the new match values are equal to 0
or the PWM rate, and there was no old match value equal to 0.
4. If both a set and a clear of a PWM output are requested at the same time, clear takes
precedence. This can occur when the set and clear match values are the same as in,
or when the set or clear value equals 0 and the other value equals the PWM rate.
5. If a match value is out of range (i.e. greater than the PWM rate value), no match event
occurs and that match channel has no effect on the output. This means that the PWM
output will remain always in one state, allowing always low, always high, or
"no change" outputs.
gives a brief summary of each of PWM related pins.
Type
Output
Output
Output
Output
Output
Output
Rev. 01 — 15 August 2005
Description
Output from PWM channel 1.
Output from PWM channel 2.
Output from PWM channel 3.
Output from PWM channel 4.
Output from PWM channel 5.
Output from PWM channel 6.
UM10139
Chapter 16: PWM
Table 247
below.
© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
257
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