Freescale Semiconductor Demonstration Board for Freescale MC9S12XHY256 Microcontroller DEMO9S12XHY256 DEMO9S12XHY256 Manual De Usuario

Freescale Semiconductor

691

The PWM duty cycle for the motor controller channel x can be determined by dividing the decimal
representation of bits D[10:0] in MCDCx by the decimal representation of the bits P[10:0] in MCPER and
multiplying the result by 100% as shown in the equation below:

x = PWM Channel Number = 0, 1, 2, 3 ... 8. This equation is only valid if
DUTY <= MCPER and MCPER is not equal to 0.

Whenever D[10:0] >= P[10:0], a constant low level (RECIRC = 0) or high level (RECIRC = 1) will be
output.

 shows how the PWM motor controller timer counter clock source is selected.

The peripheral bus clock is the source for the motor controller counter prescaler. The motor controller
counter clock rate, f

TC

, is set by selecting the appropriate prescaler value. The prescaler is selected with

the MCPRE[1:0] bits in motor controller control register 0 (MCCTL0). The motor controller channel
frequency of operation can be calculated using the following formula if DITH = 0:

Effective PWM Channel X % Duty Cycle

DUTY

MCPER

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

100%

⋅

=

 1
1/2
1/4
1/8

Motor Controller Timer

Counter Prescaler

Motor Controller

Timer

Counter Clock

Prescaler Select

MPPRE0, MPPRE1

11-Bit Motor Controller

Timer Counter

Peripheral

Bus

Clock f

BUS

Clock

Generator

CLK

Clocks and
Reset
Generator
Module

Motor Controller Timer
Counter Clock f

TC

Motor Channel Frequency (Hz)

f

TC

MCPER M

⋅

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=