
MC68F375
CONFIGURABLE TIMER MODULE (CTM9)
MOTOROLA
REFERENCE MANUAL
Rev. 25 June 03
13-48
13.7.13.2 PWMA — PWM Period Register
The PWMA register contains the period value for the next cycle of the PWM output
waveform. In normal usage, with the PWMSM enabled, the software writes a period
value into PWMA1 and this value is then loaded into the PWMA2 register at the end
of the current period. If the PWMSM is disabled, a period value written to PWMA1 is
loaded into PWMA2 on the next tic (of the MCU system clock). PWMA2 is a temporary
register that is used for smoothly updating the PWM period value; it cannot be read or
written directly by software.
Software may write a new period value into PWMA1 at any time and this new value
will take effect at the start of the next PWM period (or when the LOAD bit in the PWM-
SIC register is written to a ‘1’). The PWMSM hardware does not modify the contents
of PWMA1 at any time.
Table 13-16 PWMSM Output Pin Polarity Selection
Control Bits
Output Pin State
Periodic Edge
Variable Edge
Optional Interrupt
On
POL
EN
0
Always low
———
1
0
Always high
—
0
1
High pulse
Rising edge
Falling edge
Rising edge
1
Low pulse
Falling edge
Rising edge
Falling edge
Table 13-17 PWMSM Clock Rate Selection
PWMSM CLK Bits
CPSM Bit DIV23
PWMSM Clock
Clock Source
CLK2
CLK1
CLK0
00
0
fSYS / 2
PCLK1
00
1
0
fSYS / 4
Prescaler (/2)
01
0
fSYS / 8
Prescaler (/4)
01
1
0
fSYS / 16
Prescaler (/8)
10
0
fSYS / 32
Prescaler (/16)
10
1
0
fSYS / 64
Prescaler (/32)
11
0
fSYS / 128
Prescaler (/64)
11
1
0
fSYS / 512
Prescaler (/256)
00
0
1
fSYS / 3
PCLK1
00
1
fSYS / 6
Prescaler (/2)
01
0
1
fSYS / 12
Prescaler (/4)
01
1
fSYS / 24
Prescaler (/8)
10
0
1
fSYS / 48
Prescaler (/16)
10
1
fSYS / 96
Prescaler (/32)
11
0
1
fSYS / 192
Prescaler (/64)
11
1
fSYS / 768
Prescaler (/256)
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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