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UM10316_0
© NXP B.V. 2008. All rights reserved.
User manual
Rev. 00.06 — 17 December 2008
438 of 571
NXP Semiconductors
UM10316
Chapter 25: LPC29xx Pulse Width Modulator (PWM)
5.4 PWM capture control register
The APB PWM has three capture registers, and the capture behavior of the associated
CAPT registers and pins is controlled by the CAPCTL register. The CNT register value is
captured synchronously with the system clock.
shows the bit assignment of the CAPCTL register.
5.5 PWM capture source register
Each PWM has four capture channels, channels 2 and 3 being on the same external pin
so that in effect there are only three external capture sources per PWM. The capture
source for each channel can be selected between the external PWMx CAPTy and PWMx
TRAP pins, and the internal sync_in and the trans_enable_in signals.
shows the bit assignment of the CAPSRC register.
Table 349. CAPCTL register bit description
* = reset value
Bit
Symbol
Access
Value
Description
31 to 6
reserved
R
-
Reserved; do not modify. Read as logic 0
5 and 4
CAPT_EDGE2[1:0]
R/W
Select the edge of the capture channel 2 to
trigger capture of the PWM
00*
No triggering
01
Triggering on rising edge
10
Triggering on falling edge
11
Triggering on both edges
:
:
:
:
:
1 and 0
CAPT_EDGE0[1:0]
R/W
Select the edge of the capture channel 0 to
trigger capture of the PWM
00*
No triggering
01
Triggering on rising edge
10
Triggering on falling edge
11
Triggering on both edges
Table 350. CAPSRC register bit description
* = reset value
Bit
Symbol
Access
Value
Description
31 to 8
reserved
R
-
Reserved; do not modify. Read as logic 0
7 and 6
CAPT_SRC3[1:0]
R/W
Select the source of capture channel 3 to
trigger capture of the PWM
00*
PWMx CAPT3 signal, x is index of PWM
01
sync_in signal
10
PWMx TRAP signal, x is index of PWM
11
Trans_enable_in signal
:
:
:
:
: