LPC2142 datasheet(20/39 Pages) NXP

20 / 39 page

LPC2141_42_44_46_48_3

Product data sheet

Rev. 03 — 19 October 2007

20 of 39

NXP Semiconductors

LPC2141/42/44/46/48

Single-chip 16-bit/32-bit microcontrollers

• Ultra-low power design to support battery powered systems

• Provides Seconds, Minutes, Hours, Day of Month, Month, Year, Day of Week, and Day

of Year

• Can use either the RTC dedicated 32 kHz oscillator input or clock derived from the

external crystal/oscillator input at XTAL1, programmable reference clock divider

allows ﬁne adjustment of the RTC

• Dedicated power supply pin can be connected to a battery or the main 3.3 V

6.18 Pulse width modulator

The PWM is based on the standard timer block and inherits all of its features, although

only the PWM function is pinned out on the LPC2141/42/44/46/48. The timer is designed

to count cycles of the peripheral clock (PCLK) and optionally generate interrupts or

perform other actions when speciﬁed timer values occur, based on seven match registers.

The PWM function is also based on match register events.

The ability to separately control rising and falling edge locations allows the PWM to be

used for more applications. For instance, multi-phase motor control typically requires three

non-overlapping PWM outputs with individual control of all three pulse widths and

positions.

Two match registers can be used to provide a single edge controlled PWM output. One

match register (MR0) controls the PWM cycle rate, by resetting the count upon match.

The other match register controls the PWM edge position. Additional single edge

controlled PWM outputs require only one match register each, since the repetition rate is

the same for all PWM outputs. Multiple single edge controlled PWM outputs will all have a

rising edge at the beginning of each PWM cycle, when an MR0 match occurs.

Three match registers can be used to provide a PWM output with both edges controlled.

Again, the MR0 match register controls the PWM cycle rate. The other match registers

control the two PWM edge positions. Additional double edge controlled PWM outputs

require only two match registers each, since the repetition rate is the same for all PWM

outputs.

With double edge controlled PWM outputs, speciﬁc match registers control the rising and

falling edge of the output. This allows both positive going PWM pulses (when the rising

edge occurs prior to the falling edge), and negative going PWM pulses (when the falling

edge occurs prior to the rising edge).

6.18.1 Features

• Seven match registers allow up to six single edge controlled or three 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

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