P912XDP512F0MPVR datasheet(379/1348 Pages) FREESCALE

379 / 1348 page

Chapter 8 Pulse-Width Modulator (S12PWM8B8CV1)

MC9S12XDP512 Data Sheet, Rev. 2.21

Freescale Semiconductor

379

NOTE

Reads of this register return the most recent value written. Reads do not

necessarily return the value of the currently active duty due to the double

buffering scheme.

See Section 8.4.2.3, “PWM Period and Duty” for more information.

NOTE

Depending on the polarity bit, the duty registers will contain the count of

either the high time or the low time. If the polarity bit is one, the output starts

high and then goes low when the duty count is reached, so the duty registers

contain a count of the high time. If the polarity bit is zero, the output starts

low and then goes high when the duty count is reached, so the duty registers

contain a count of the low time.

To calculate the output duty cycle (high time as a% of period) for a particular channel:

•

Polarity = 0 (PPOL x =0)

Duty Cycle = [(PWMPERx-PWMDTYx)/PWMPERx] * 100%

•

Polarity = 1 (PPOLx = 1)

Duty Cycle = [PWMDTYx / PWMPERx] * 100%

For boundary case programming values, please refer to Section 8.4.2.8, “PWM Boundary Cases”.

Read: Anytime

Write: Anytime

8.3.2.15

PWM Shutdown Register (PWMSDN)

The PWMSDN register provides for the shutdown functionality of the PWM module in the emergency

cases. For proper operation, channel 7 must be driven to the active level for a minimum of two bus clocks.

Read: Anytime

Write: Anytime

76543210

Bit 7

Bit 0

Reset

11111111

Figure 8-16. PWM Channel Duty Registers (PWMDTYx)

76543210

PWMIF

PWMIE

PWMLVL

PWM7IN

PWM7INL

PWM7ENA

PWMRSTRT

Reset

00000000

= Unimplemented or Reserved

Figure 8-17. PWM Shutdown Register (PWMSDN)

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