mc9s12e256 Freescale Semiconductor, Inc, mc9s12e256 Datasheet - Page 396

• Manufacturer Part Number: mc9s12e256
• Description: Hcs12 Microcontrollers 16-bit Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

Chapter 12 Pulse-Width Modulator (PWM8B6CV1)
Read: anytime
Write: anytime
12.3.2.14 PWM Channel Duty Registers (PWMDTYx)
There is a dedicated duty register for each channel. The value in this register determines the duty of the
associated PWM channel. The duty value is compared to the counter and if it is equal to the counter value
a match occurs and the output changes state.
The duty registers for each channel are double buffered so that if they change while the channel is enabled,
the change will NOT take effect until one of the following occurs:
In this way, the output of the PWM will always be either the old duty waveform or the new duty waveform,
not some variation in between. If the channel is not enabled, then writes to the duty register will go directly
to the latches as well as the buffer.
Reference
To calculate the output duty cycle (high time as a % of period) for a particular channel:
396
Reset
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•
•
•
•
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W
R
The effective period ends
The counter is written (counter resets to 0x0000)
The channel is disabled
Polarity = 0 (PPOLx = 0)
Polarity = 1 (PPOLx = 1)
For boundary case programming values, please refer to
Duty cycle = [(PWMPERxšPWMDTYx)/PWMPERx] * 100%
Duty cycle = [PWMDTYx / PWMPERx] * 100%
Section 12.4.2.3, “PWM Period and Duty,”
Bit 7
0
7
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.
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 1, 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 0, 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.
Figure 12-26. PWM Channel Period Registers (PWMPER5)
6
0
6
MC9S12E256 Data Sheet, Rev. 1.08
5
0
5
NOTE
NOTE
4
0
4
for more information.
Section 12.4.2.8, “PWM Boundary Cases.”
3
3
0
2
0
2
Freescale Semiconductor
1
0
1
Bit 0
0
0