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TIMER A

7721 Group User’s Manual

8–34

8.5 One-shot pulse mode

8.5.3 Trigger

The counter is enabled for counting when the count start bit (address 4016) is set to “1.” The counter starts

counting when a trigger is generated after counting has been enabled. An internal or external trigger can

be selected as that trigger.

An internal trigger is selected when the trigger select bits (bits 4 and 3 at addresses 5816 to 5A16) are “002”

or “012”; an external trigger is selected when the bits are “102” or “112.”

If a trigger is generated during counting, the reload register’s contents are reloaded and the counter

continues counting. 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.

(1)

When selecting internal trigger

A trigger is generated when writing “1” to the one-shot start bit (bits 2 to 4 at address 4216). Figure

8.5.4 shows the structure of the one-shot start register.

(2)

When selecting external trigger

A trigger is generated at the falling edge of the TAjIN pin’s input signal when bit 3 at addresses 5816

to 5A16 is “0,” or at its rising edge when bit 3 is “1.”

When using an external trigger, set the port P5 direction registers’ bits which correspond to the TAjIN

pins for the input mode.

Fig. 8.5.4 Structure of one-shot start register

Bit

7 to 5 Nothing is assigned.

Timer A4 one-shot start bit

Timer A3 one-shot start bit

Timer A2 one-shot start bit

Bit name

At reset

Undefined

Functions

One-shot start register (Address 4216)

1 : Start outputting one-shot pulse

(valid when internal trigger is

selected.)

The value is “0” at reading.

–

Fix these bits to “0.” The value is “0” at reading.

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