7906 datasheet(118/531 Pages) RENESAS

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TIMER A

7906 Group User’s Manual Rev.2.0

7-15

7.3 Timer mode

7.3.3 Select function

In timer Aj (j = 0 to 2, 4, 9), the gate function or pulse output function can be selected.

The following describes the gate and pulse output functions.

(1)

Gate function

The gate function is selected by setting the gate function select bits (bits 4 and 3 at addresses 5616

to 5816, 5A16, DA16) to “102” or “112.” The gate function makes it possible to start or stop counting

depending on the TAjIN pin’s input signal. Table 7.3.2 lists the count valid levels.

Figure 7.3.4 shows an example of operation with the gate function selected.

When selecting the gate function, set the port P2 and port P6 direction registers’ bits which correspond

to the TAjIN pins 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 7.3.2 Count valid levels

Gate function select bits

Count valid level (Duration while counter counts)

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

While TAjIN pin’s input signal level 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. 7.3.4 Example of operation with gate function selected

FFFF16

000016

Time

➀ Starts counting.

➁ 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.

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

➁ 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

n : Reload register’s contents

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