LPC2109 datasheet(20/46 Pages) NXP

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LPC2109_2119_2129

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Product data sheet

Rev. 7 — 14 June 2011

20 of 46

NXP Semiconductors

LPC2109/2119/2129

Single-chip 16/32-bit microcontrollers

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).

6.17.1 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.

• 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.

6.18 System control

6.18.1 Crystal oscillator

The oscillator supports crystals in the range of 1 MHz to 30 MHz. The oscillator output

frequency is called fosc and the ARM processor clock frequency is referred to as CCLK for

purposes of rate equations, etc.. fosc and CCLK are the same value unless the PLL is

running and connected. Refer to Section 6.18.2 “PLL” for additional information.

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