C8051F52X_12 Datasheet, PDF(203/221 Page) Silicon Laboratories – 8/4/2 kB ISP Flash MCU Family

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C8051F52X_12 Datasheet, PDF (203/221 Pages) Silicon Laboratories – 8/4/2 kB ISP Flash MCU Family

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C8051F52x/F53x

19.2.6. 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

register. For a varying duty cycle, match interrupts should be enabled (ECCFn = 1 AND MATn = 1) to help

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

Equation 19.3.

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

ture/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.

DutyCycle = ï¨---6---5---5---3---6----â-----P----C----A----0----C----P----n----ï©

65536

Equation 19.3. 16-Bit PWM Duty Cycle

Using Equation 19.3, 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.

PCA0CPMn

P ECCMT P E

WCA A AOWC

MOPP TGMC

1 MPN n n n F

6nnn

n

n

1 0000 0

PCA0CPHn PCA0CPLn

Enable

16-bit Comparator

match S SET Q

CEXn Crossbar

Port I/O

PCA Timebase

PCA0H

PCA0L

Overflow

RQ

CLR

Figure 19.9. PCA 16-Bit PWM Mode

19.3. Watchdog Timer Mode

A programmable watchdog timer (WDT) function is available through the PCA Module 2. The WDT is used

to generate a reset if the time between writes to the WDT update register (PCA0CPH2) exceed a specified

limit. The WDT can be configured and enabled/disabled as needed by software.

With the WDTE bit set in the PCA0MD register, Module 2 operates as a watchdog timer (WDT). The

Module 2 high byte is compared to the PCA counter high byte; the Module 2 low byte holds the offset to be

used when WDT updates are performed. The Watchdog Timer is enabled on reset. Writes to some

PCA registers are restricted while the Watchdog Timer is enabled.

Rev. 1.4

203

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