UM10360 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
User manual Rev. 3 — 19 December 2013 511 of 841
NXP Semiconductors
UM10360
Chapter 24: LPC176x/5x Pulse Width Modulator (PWM)
24.3 Description
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 LPC176x/5x. 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 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 an 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).
Figure 119
shows the block diagram of the PWM. The portions that have been added to
the standard timer block are on the right hand side and at the top of the diagram.
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