mc68hc908mr8 Freescale Semiconductor, Inc, mc68hc908mr8 Datasheet - Page 148

• Manufacturer Part Number: mc68hc908mr8
• Description: M68hc08 Microcontrollers Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

Pulse-Width Modulator for Motor Control
9.4.2 Prescaler
9.5 PWM Generators
9.5.1 Load Operation
Technical Data
148
To permit lower PWM frequencies, a prescaler is provided which will
divide the PWM clock frequency by 1, 2, 4, or 8.
setting the prescaler bits in PWM control register 2 affects the PWM
clock frequency. This prescaler is buffered and will not be used by the
PWM generator until the LDOK bit is set and a new PWM reload-cycle
begins.
This subsection describes the pulse-width modulator (PWM) generators.
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:LDFQ0 in PWM control register 2 are used to control this reload
frequency, as shown in
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.
Pulse-Width Modulator for Motor Control (PWMMC)
PRSC1:PRSC0
Prescaler Bits
00
01
10
11
Table 9-1. PWM Prescaler
Table
9-2. When a reload cycle arrives,
PWM Clock Frequency
f
f
f
OP
OP
OP
f
OP
MC68HC908MR8 — Rev 4.1
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Table 9-1
Freescale Semiconductor
shows how