Datasheet

Product data sheet Rev. 5.1 — 16 October 2013 26 of 66

NXP Semiconductors

LPC2387

Single-chip 16-bit/32-bit MCU

– Do nothing on match.

7.21 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 LPC2387. The Timer is designed to count

cycles of the system derived clock and optionally switch pins, generate interrupts or

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

The PWM function is in addition to these features, and is 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 (PWMMR0) 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 a PWMMR0 match occurs.

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

Again, the PWMMR0 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).

7.21.1 Features

• LPC2387 has one PWM block with 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.