7721 datasheet(134/577 Pages) RENESAS

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TIMER A

7721 Group User’s Manual

8–15

8.3 Timer mode

8.3.4 Selectable functions

The following describes the selectable gate function for Timers A2 to A4 and pulse output function.

(1)

Gate function

The gate function is selected by setting the gate function select bits (bits 4 and 3 at addresses 5816

to 5A16 ) to “102” or “112.” The gate function makes it possible to start or stop counting depending on

the TAjIN pin’s input signal. Table 8.3.3 lists the count valid levels. Figure 8.3.5 shows an example

of operation with the gate function selected.

When selecting the gate function, set the port P5 direction registers’ bits which correspond to the

TAjIN pin for the input mode. Additionally, make sure that the TAjIN pin’s input signal has a pulse width

equal to or more than two cycles of the count source.

Table 8.3.3 Count valid levels

Gate function select bits

Count valid level (Duration while counter counts)

While TAjIN pin’s input signal is at “L” level

While TAjIN pin’s input signal is at “H” level

Note: The counter does not count while the TAjIN pin’s input signal is not at the count valid level.

Fig. 8.3.5 Example of operation selecting gate function

FFFF16

000016

Time

Starts counting.

n = Reload register’s contents

Stops counting.

Set to “1” by software.

Count start bit

TAjIN pin’s

input signal

Count valid

level

Timer Aj interrupt

request bit

Cleared to “0” when

interrupt request is

accepted or cleared

by software.

The counter counts when the count start bit = “1” and the TAjIN pin’s input signal is at the count valid

level.

The counter stops counting while the TAjIN pin’s input signal is not at the count valid level, and the

counter value is retained.

Invalid level

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