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Chapter 4 Timer Functions
If the TM3PWM flag of the TM3MD
register is set to "1" and timer 2
PWM output is selected, the PWM
output of timer 2 will also be output
from the TM3IO pin.
If port 1 is to be used as a PWM
output pin, the P1DIR and P1PLU
registers must be set.
66
8-bit Timer Operation (timers 2, 3)
PWM Output Function (Timer 2)
Settings for the PWM output function are listed below.
(1)
Set the TM2EN flag of the timer 2 mode register (TM2MD) to "0" to stop the count
operation of timer 2.
(2)
Set bit 2 of the port 1 output/input mode register (P1OMD) to the special function
pin setting. Bit 2 of port 1 will be specified as the PWM output pin.
(3)
Set the TM2CK2 to 0 flags of the TM2MD register to select fs, fs/4, fx, or
synchronous fx as the clock source. The period of the output waveform is determined
based on the clock source.
(4)
Set the TM2PWM flag of the TM2MD register to "1" so that PWM operation is
selected.
(5)
Set a value in compare register 2 (TM2OC). The high interval of the output
waveform is determined based on the value of the TM2OC compare register.
(6)
Set the TM2EN flag of the TM2MD register to "1" to start the timer.
(7)
When timer 2 begins operation, binary counter 2 will count upward from X'00'.
(8)
A high-level signal is output from the port beginning when binary counter 2 starts
counting at X'00' and ending when the value of binary counter 2 matches the value
set in the TM2OC register.
(9)
When the value of binary counter 2 matches that of the TM2OC register, a low-level
signal is output from the port.
(10)
Binary counter 2 continues to count upward until X'FF' is reached. At the next count-
up cycle, the value of binary counter 2 is reset to X'00', a high-level signal is output
from the port, and counting begins again.
Binary
counter 2
PWM output
Figure 4-2-4 PWM Output Timing
Matches TM2OC
register
Time specified by TM2OC register
Time until binary counter 2 reaches X'FF'
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