UM10413
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User manual
Rev. 1 — 16 December 2011
187 of 268
NXP Semiconductors
UM10413
MPT612 User manual
21.5.13 Rules for single edge-controlled PWM outputs
•
All single edge-controlled PWM outputs go LOW at the beginning of each PWM cycle
(timer is set to zero) unless their match value is equal to zero.
•
Each PWM output goes HIGH when its match value is reached. If no match occurs
(that is, the match value is greater than the PWM cycle length), the PWM output
remains continuously LOW.
•
If a match value larger than the PWM cycle length is written to the match register, and
the PWM signal is HIGH already, then the PWM signal is cleared with the start of the
next PWM cycle.
•
If a match register contains the same value as the timer reset value (the PWM cycle
length), then the PWM output is reset to LOW on the next clock tick after the timer
reaches the match value. Therefore, the PWM output always consists of a one clock
tick wide positive pulse with a period determined by the PWM cycle length (that is, the
timer reload value).
•
If a match register is set to zero, then the PWM output goes HIGH the first time the
timer returns to zero and stays HIGH continuously
Remark:
If the match outputs are selected to perform as PWM outputs, the timer reset
(MRnR) and timer stop (MRnS) bits in the match control register MCR must be set to zero
except for the match register setting the PWM cycle length. For this register, set bit MRnR
to logic 1 to enable the timer reset when the timer value matches the value of the
corresponding match register.
Table 174: PWM Control register (PWMCON, TIMER1: PWM1CON - address 0xE000 8074) bit
description
Bit
Symbol
Description
Reset value
0
PWM enable
if logic 1, PWM mode is enabled for MATn.0. If logic 0,
MATn.0 is controlled by EM0
0
1
PWM enable
if logic 1, PWM mode is enabled for MATn.1. If logic 0,
MATn.1 is controlled by EM1
0
2
PWM enable
if logic 1, PWM mode is enabled for MATn.2. If logic 0,
MATn.2 is controlled by EM2
0
3
PWM enable
if 1, PWM mode is enabled for MATn.3. If logic 0,
MATn.3 is controlled by EM3.
0
4:32
-
reserved, user software must not write logic 1s to
reserved bits; value read from a reserved bit is not
defined
n/a