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TIMER A

7733 Group User’s Manual

6–47

6.6.4 Operation in PWM mode

When the PWM mode is selected by the operating mode selection bits, pin TAiOUT outputs “L” level.

When a trigger occurs, the counter (Pulse width modulator) starts counting and pin TAiOUT outputs a

PWM pulse (Notes 1 and 2).

A timer Ai interrupt request bit is set to “1” each time the PWM pulse level changes from “H” to “L.”

After this, the interrupt request bit remains set to “1” until the interrupt request is accepted or the

interrupt request bit is cleared to “0” by software.

Each time a PWM pulse is output for one period, the reload register’s contents is reloaded and counting

is continued.

Operation of the pulse width modulator is described below.

[16-bit pulse width modulator]

When the 16/8-bit PWM mode selection bit is set to “0,” the counter operates as a 16-bit pulse width

modulator. Each of Figures 6.6.4 and 6.6.5 shows an operation example of the 16-bit pulse width modulator.

[8-bit pulse width modulator]

When the 16/8-bit PWM mode selection bit is set to “1,” the counter is divided into 8-bit halves. Then, the

high-order 8 bits operate as an 8-bit pulse width modulator, and the low-order 8 bits operate as an 8-bit

prescaler. Each of Figures 6.6.6 and 6.6.7 shows an operation example of the 8-bit pulse width modulator.

Notes 1: If a value of “000016” is set in the timer Ai register when the counter operates as a 16-bit pulse

width modulator, the pulse width modulator does not operate and the output level of pin TAiOUT

remains “L.” Nor is a timer Ai interrupt request generated. These operations are also applied to

the case where a value of “0016” is set in high-order 8 bits of the timer Ai register when the

counter operates as an 8-bit pulse width modulator.

2: When the counter operates as an 8-bit pulse width modulator, after a trigger occurs, pin TAiOUT

outputs “L” level of which width is the same as the PWM pulse’s “H” level width which was set.

And then, pin TAiOUT starts the PWM pulse output.

6.6 Pulse width modulation (PWM) mode

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