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1
8.
Overview of Pulse Width Count Timer
The pulse width count timer (PWC) can be selected to function as either an interval
timer or the pulse width measurement. The interval timer function counts down in
sync with one of three internal count clocks. The pulse width measurement function
measures the width of pulses input to an external pin.
Therefore, an 8-bit interval timer time can be set and the output can be used to
generate variable frequency square wave output. Also, the PWC can be used as an
input capture by continuously measuring the pulse width of an external input.
n Interval Timer Function (Square Wave Output Function)
The interval timer function generates repeated interrupts at variable time intervals.
Also, as the PWC can invert the output level of the pin (WTO pin) each time interval, the PWC
can output a variable frequency square wave.
•
The interval timer can operate with a cycle among 1 and 2
cycle.
•
The internal count clock can be selected from three different clocks.
•
Two operating modes are available: reload timer mode (continuous operation) and one-shot
mode (one-time operation).
•
The timer output bit (PCR2: TO) can be used as the count clock for the 8-bit PWM timer.
Table 8.1a lists the available interval time and square wave output ranges.
Table 8.1a Interval Time and Square Wave Output Range
Internal count clock cycle
t
: Instruction cycle (divide-by-four source oscillation)
inst
158
CHAPTER 8 PULSE WIDTH COUNT TIMER (PWC)
1 t
inst
4 t
inst
32 t
inst
8
times the internal count clock
Interval time
t
1 t
to 2
8
inst
inst
2
t
10
t
2
to 2
inst
inst
t
t
2
5
to 2
13
inst
inst
Square wave output (Hz)
t
1/(2 t
) to 1/(2
9
)
inst
inst
3
t
11
t
1/(2
) to 1/(2
)
inst
inst
t
t
1/(2
6
) to 1/(2
14
)
inst
inst
MB89620 series
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