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TIMER A

7721 Group User’s Manual

8–35

8.5 One-shot pulse mode

8.5.4 Operation in one-shot pulse mode

When the one-shot pulse mode is selected with the operating mode select bits, the TAjOUT pin outputs

“L” level.

When the count start bit is set to “1,” the counter is enabled for counting. After that, counting starts when

a trigger is generated.

When the counter starts counting, the TAjOUT pin outputs “H” level.

When the counter value becomes “000016,” the output from the TAjOUT pin becomes “L” level. Additionally,

the reload register’s contents are reloaded and the counter stops counting there.

Simultaneously with , the timer Aj interrupt request bit is set to “1.”

This interrupt request bit remains set to “1” until the interrupt request is accepted or the interrupt request

bit is cleared to “0” by software.

Figure 8.5.5 shows an example of operation in the one-shot pulse mode.

When a trigger is generated after above, the counter and TAjOUT pin perform the same operations

beginning from again. Furthermore, if a trigger is generated during counting, the counter performs

countdown once after this new trigger is generated, and it continues counting with the reload register’s

contents reloaded. If generating a trigger during counting, make sure that a certain time which is equivalent

to one cycle of the timer’s count source or more has passed between the previously generated trigger and

a new trigger.

The one-shot pulse output from the TAjOUT pin can be disabled by clearing the timer Aj mode register’s bit

2 to “0.” Accordingly, Timer Aj can be also used as an internal one-shot timer that does not perform the

pulse output. In this case, the TAjOUT pin functions as a programmable I/O port.

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