
CTM
REFERENCE
MOTOROLA
9-11
PULSE WIDTH MODULATION SUBMODULE
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9
LOAD — Period and pulse width register load control bit
The LOAD bit is a control bit that allows the software to reinitialize the PWMSM and start a new
PWM period without causing a glitch on the PWM output signal.
1 (set)
–
Load period and pulse width registers.
0 (clear) –
No action.
This bit is always read as a zero. Writing a one to this bit results in the following immediate actions:
–
–
–
–
–
–
the contents of PWMA1 (period value) are transferred to PWMA2,
the contents of PWMB1 (pulse width value) are transferred to PWMB2,
the counter register (PWMC) is initialized to $0001,
the control logic and state sequencer are reset,
the FLAG bit is set, and
the output flip-flop is set if the new value in PWMB2 is different from $0000.
Note:
Writing a one to the LOAD bit when the EN bit = 0, i.e. when the PWMSM is disabled,
has no effect.
POL — Output pin polarity control bit
The POL bit is a control bit that allows the software to set the polarity of the PWM output signal. It
works in conjunction with the EN bit and controls whether the PWMSM drives the output pin with
the true or inverted value of the output flip-flop (see Table 9-4).
Table 9-4
PWMSM output pin polarity selection
Control bits
POL
0
1
0
1
Output pin state
Periodic edge
Variable edge
Optional
interrupt on
—
—
Rising edge
Falling edge
EN
0
0
1
1
Always low
Always high
High pulse
Low pulse
—
—
—
—
Rising edge
Falling edge
Falling edge
Rising edge
F
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Freescale Semiconductor, Inc.