pc87591l-n05 National Semiconductor Corporation, pc87591l-n05 Datasheet - Page 143

• Manufacturer Part Number: pc87591l-n05
• Description: Lpc Mobile Embedded Controller
• Manufacturer: National Semiconductor Corporation

Revision 1.2
4.0 Embedded Controller Modules
4.8
The PWM module generates eight 8/16-bit PWM outputs; each may have a different duty cycle. A common 8/16-bit clock
pre-scaler and an 8/16-bit down-counter determine the cycle time, the minimal possible pulse width and the duty cycle steps.
The PWM is configurable to provide 8-bit or 16-bit resolution PWM outputs, as defined by PWMRES bit of PWM Control
Register (PWMCNT).
4.8.1
4.8.2
The PWM generates eight 8/16-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 1:65536, 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 8/16-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 50 is a functional block diagram of the PWM module.
• Eight PWM outputs
• Common 8/16-bit fully programmable pre-scaler
• Common 8/16-bit fully programmable down-counter
• 8/16-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
Pre-Scaler Register
Pre-Scaler Counter
INVPi
8/16 Bit, Compare
8/16 Bit, Clock
Duty Cycle
Register 0
8/16 Bit,
8/16 Bit,
Figure 50. PWM Block Diagram
(Continued)
Cycle Time Register
Down-Counter
143
8/16 Bit,
8/16 Bit,
8/16 Bit, Compare
Duty Cycle
Register 7
8/16 Bit,
Down-Counter == CTR
PWM7
S
Q Q
0
R
1
INVPi
www.national.com