MC68HC908LB8_05 Datasheet, PDF (146/234 Pages) Freescale Semiconductor, Inc – M68HC08 Microcontrollers

Pulse Width Modulator with Fault Input (PWM)
Table 15-1. PWM Prescaler
Prescaler Bits
PRSC1 and PRSC0
00
01
10
11
PWM Clock Frequency
BUSCLK
BUSCLK/2
BUSCLK/4
BUSCLK/8
15.4 PWM Generators
Pulse-width modulator (PWM) generators are discussed in this subsection.
15.4.1 Load Operation
To help avoid erroneous pulse widths and PWM periods, the modulus, prescaler, and PWM value
registers are buffered. New PWM values, counter modulus values, and prescalers can be loaded from
their buffers into the PWM module every one, two, four, or eight PWM cycles. LDFQ1 and LDFQ0 in PWM
control register 2 are used to control this reload frequency, as shown in Table 15-2. When a reload cycle
arrives, regardless of whether an actual reload occurs (as determined by the LDOK bit), the PWM reload
flag bit in PWM control register 1 will be set. If the PWMINT bit in PWM control register 1 is set, a CPU
interrupt request will be generated when PWMF is set. Software can use this interrupt to calculate new
PWM parameters in real time for the PWM module.
Table 15-2. PWM Reload Frequency
Reload Frequency Bits
LDFQ1 and LDFQ0
00
01
10
11
PWM Reload Frequency
Every PWM cycle
Every 2 PWM cycles
Every 4 PWM cycles
Every 8 PWM cycles
MC68HC908LB8 Data Sheet, Rev. 1
146
Freescale Semiconductor