C8051F310 datasheet(211/228 Pages) SILABS

211 / 228 page

Rev. 1.7

211

C8051F310/1/2/3/4/5/6/7

18.2.6. 16-Bit Pulse Width Modulator Mode

A PCA module may also be operated in 16-Bit PWM mode. In this mode, the 16-bit capture/compare mod-

ule defines the number of PCA clocks for the low time of the PWM signal. When the PCA counter matches

the module contents, the output on CEXn is asserted high; when the counter overflows, CEXn is asserted

low. To output a varying duty cycle, new value writes should be synchronized with PCA CCFn match inter-

rupts. 16-Bit PWM Mode is enabled by setting the ECOMn, PWMn, and PWM16n bits in the PCA0CPMn

synchronize the capture/compare register writes. The duty cycle for 16-Bit PWM Mode is given by

Equation 18.3.

Important Note About Capture/Compare Registers: When writing a 16-bit value to the PCA0 Capture/

Compare registers, the low byte should always be written first. Writing to PCA0CPLn clears the ECOMn bit

to ‘0’; writing to PCA0CPHn sets ECOMn to ‘1’.

Using Equation 18.3, the largest duty cycle is 100% (PCA0CPn = 0), and the smallest duty cycle is

0.0015% (PCA0CPn = 0xFFFF). A 0% duty cycle may be generated by clearing the ECOMn bit to ‘0’.

Figure 18.9. PCA 16-Bit PWM Mode

Equation 18.3. 16-Bit PWM Duty Cycle

DutyCycle

65536

PCA0CPn

–

()

65536

-----------------------------------------------------

PCA0CPLn

PCA0CPHn

Enable

PCA Timebase

00 x 0

PCA0CPMn

16-bit Comparator

CEXn

Crossbar

Port I/O

Overflow

SET

CLR

match

PCA0H

PCA0L

ENB

Write to

PCA0CPLn

Write to

PCA0CPHn

Reset

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