NXP Semiconductors LPC1751, Руководство пользователя, Страница: 481 / 808

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UM10360_0 © NXP B.V. 2009. All rights reserved.
User manual Rev. 00.06 — 5 June 2009 481 of 808
1. Basic configuration
The PWM is configured using the following registers:
1. Power: In the PCONP register ( Table 4–46 ), set bit PCPWM1.
Remark: On reset, the PWM is enabled (PCPWM1 = 1).
2. Peripheral clock: In the PCLKSEL0 register ( Table 4–40 ), select PCLK_PWM1.
3. Pins: Select PWM pins through the PINSEL registers. Select pin modes for port pins
with PWM1 functions through the PINMODE registers ( Section 8–5 ).
4. Interrupts: See registers PWM1MCR ( Table 24–431 ) and PWM1CCR ( Table 24–432 )
for match and capture events. Interrupts are enabled in the NVIC using the
appropriate Interrupt Set Enable register.
2. Features
•
Counter or Timer operation (may use the peripheral clock or one of the capture inputs
as the clock source).
•
Seven match registers allow up to 6 single edge controlled or 3 double edge
controlled PWM outputs, or a mix of both types. The match registers also allow:
– Continuous operation with optional interrupt generation on match.
– Stop timer on match with optional interrupt generation.
– Reset timer on match with optional interrupt generation.
•
Supports single edge controlled and/or double edge controlled PWM outputs. Single
edge controlled PWM outputs all go high at the beginning of each cycle unless the
output is a constant low. Double edge controlled PWM outputs can have either edge
occur at any position within a cycle. This allows for both positive going and negative
going pulses.
•
Pulse period and width can be any number of timer counts. This allows complete
flexibility in the trade-off between resolution and repetition rate. All PWM outputs will
occur at the same repetition rate.
•
Double edge controlled PWM outputs can be programmed to be either positive going
or negative going pulses.
•
Match register updates are synchronized with pulse outputs to prevent generation of
erroneous pulses. Software must "release" new match values before they can
become effective.
•
May be used as a standard timer if the PWM mode is not enabled.
•
A 32-bit Timer/Counter with a programmable 32-bit prescaler.
•
Two 32-bit capture channels take a snapshot of the timer value when an input signal
transitions. A capture event may also optionally generate an interrupt.
UM10360
Chapter 24: LPC17xx Pulse Width Modulator (PWM)
Rev. 00.06 — 5 June 2009 User manual