UM11029
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User manual
Rev. 1.0 — 16 June 2017
407 of 515
NXP Semiconductors
UM11029
Chapter 21: LPC84x SCTimer/PWM
A limit event when BIDIR is 1 does not clear the prescaler. Rather it clears the DOWN bit
in the Control register, and decrements the counter on the same clock if the counter is
enabled in that clock.
21.7.8 Match vs. I/O events
Counter operation is complicated by the prescaler and by clock mode 01 in which the
SCTimer/PWM clock is the bus clock. However, the prescaler and counter are enabled to
count only when a selected edge is detected on a clock input.
•
The prescaler is enabled when the clock mode is not 01, or when the input edge
selected by the CLKSEL field is detected.
•
The counter is enabled when the prescaler is enabled, and (PRELIM=0 or the
prescaler is equal to the value in PRELIM).
An I/O component of an event can occur in any SCTimer/PWM clock when its counter
HALT bit is 0. In general, a Match component of an event can only occur in an
SCTimer/PWM clock when its counter HALT and STOP bits are both 0 and the counter is
enabled.
shows when the various kinds of events can occur.
Table 413. Event conditions
COMBMODE IOMODE
Event can occur on clock:
IO
Any
Event can occur whenever HALT = 0 (type A).
MATCH
Any
Event can occur when HALT = 0 and STOP = 0 and the counter is
enabled (type C).
OR
Any
From the IO component: Event can occur whenever HALT = 0 (A).
From the match component: Event can occur when HALT = 0 and
STOP = 0 and the counter is enabled (C).
AND
LOW or HIGH Event can occur when HALT = 0 and STOP = 0 and the counter is
enabled (C).
AND
RISE or FALL
Event can occur whenever HALT = 0 (A).