NXP Semiconductors MPC5606S - PWM Duty Cycle

Stepper Motor Controller (SMC)
MPC5606S Microcontroller Reference Manual, Rev. 7
Freescale Semiconductor 1149
35.4.2 PWM Duty Cycle
The PWM duty cycle for the SMC channel x can be determined by dividing the decimal representation of
the bits MCDCx[DUTY] by the decimal representation of the bits MCPER[PER] and multiplying the
result by 100% as shown in Equation 35-1.
Eqn. 35-1
NOTE
x = PWM Channel Number = 0, 1, 2, 3 ... 11. This equation is only valid if
MCDCx[DUTY] <= MCPER[PER] and MCPER[PER] is not equal to 0.
Whenever MCDCx[DUTY] >= MCPER[PER], a constant low level (MCCTL1[RECIRC] = 0) or high
level (MCCTL1[RECIRC] = 1) will be output.
35.4.3 Motor Controller Counter Clock Source
Figure 35-32 shows how the PWM motor controller timer counter clock source is selected.
Figure 35-32. Motor Controller Counter Clock Selection
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 MCCTL0[MCPRE] bits. The SMC channel frequency of operation can be calculated using
Equation 35-2 if MCCTL0[DITH] = 0.
Eqn. 35-2
The SMC channel frequency of operation can be calculated using Equation 35-3 if MCCTL0[DITH] = 1.
Eqn. 35-3
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
-------------------------------
=
Motor Channel Frequency (Hz)
f
TC
MCPER M 2
--------------------------------------
=