7721 datasheet(137/577 Pages) RENESAS

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TIMER A

7721 Group User’s Manual

8–18

8.4 Event counter mode

In this mode, the timer counts an external signal. (Refer to “Tables 8.4.1 and 8.4.2.”) Timers A2 to A4 can

be used in this mode. Figure 8.4.1 shows the structures of the timer Aj mode register and timer Aj register

in the event counter mode.

Table 8.4.1 Specifications of event counter mode (when not using two-phase pulse signal processing function)

Specifications

q External signal input to the TAjIN pin

q The count source’s valid edge can be selected from the falling edge

and the rising edge by software.

q Countup or countdown can be switched by external signal or software.

q When a counter overflow or underflow occurs, reload register’s contents

are reloaded, and counting continues.

q For countdown

q For countup

When the count start bit is set to “1.”

When the count start bit is cleared to “0.”

When a counter overflow or underflow occurs.

Count source input

Programmable I/O port, pulse output, or countup/countdown switch signal

input

Counter value can be read out.

q While counting is stopped

When a value is written to the timer Aj register, it is written to both

of the reload register and counter.

q While counting is in progress

When a value is written to the timer Aj register, it is written only to

the reload register. (Transferred to the counter at the next reload

time.)

Item

Count source

Count operation

Division ratio

Count start condition

Count stop condition

Interrupt request occurrence timing

TAjIN pin’s function

TAjOUT pin’s function

Read from timer Aj register

Write to timer Aj register

(n + 1)

(FFFF16 – n + 1)

n : Timer Aj register’s set value

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