pc87591l National Semiconductor Corporation, pc87591l Datasheet - Page 147

• Manufacturer Part Number: pc87591l
• Description: Lpc Mobile Embedded Controllers
• Manufacturer: National Semiconductor Corporation

Revision 1.07
Embedded Controller Modules
4.8
The PWM module generates eight 8-bit PWM outputs; each may have a different duty cycle. A common 8-bit clock pre-scaler
and an 8-bit down-counter determine the cycle time, the minimal possible pulse width and the duty cycle steps.
4.8.1
4.8.2
The PWM generates eight 8-bit PWM outputs, PWM0 to PWM7. The Duty Cycle registers 0 to 7 (DCRi, i = 0 to 7) control
the duty cycle of PWM0 to PWM7 output signals, respectively. The Cycle Time register (CTR) controls the cycle time and
duty cycle steps of all outputs.
The PWM use the core domain clock as a reference for its activities. The pre-scaler divider divides the PWM input clock by
a pre-programmable ratio of 1:1 through 1:256, as defined by the Clock Pre-Scaler register (PRSC).
The PWM cycle is defined in terms of cycles of the pre-scaler output clock. It has a period of (CTR +1) cycles, out of which
the signal will be high for DCRi cycles. INVPi, when set, may be used to inverse this behavior.
The cycle period is defined by the 8-bit down-counter. It counts using the output clock from the pre-scaler divider, starting
from the value held in CTR register down to 0. When it reaches 0, the down-counter restarts from the CTR value.
The DCRi register defines the number of clock cycles during which PWMi signal is high during the complete down-counter
cycle.
If Inverse PWMi bit (INVPi) in PWM Polarity register (PWMPOL) is active (1), the DCRi register defines the number of clock
cycles during which PWMi signal is low in each of the down-counter complete cycles.
Figure 51 is a functional block diagram of the PWM module.
Eight PWM outputs
One 8-bit fully programmable pre-scaler
One 8-bit fully programmable down-counter
8-bit duty cycle control per output
Programmable polarity per output
Low Power mode
PULSE WIDTH MODULATOR (PWM)
Features
Functional Description
Input
Clock
PWM0
Q
R
0
S
1
Q
INVPi
Clock Pre-Scaler
8-Bit Pre-Scaler
Duty Cycle
Register 0
Compare
Register
Counter
Figure 51. PWM Block Diagram
(Continued)
Down-Counter
147
Cycle Time
Register
8-Bit
Duty Cycle
Register 7
Compare
Down-Counter == CTR
PWM7
S
Q Q
0
R
1
INVPi
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