7906 datasheet(175/531 Pages) RENESAS

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7906 Group User’s Manual Rev.2.0

8-24

TIMER B

(2)

Timer Bi overflow flag

s When counter clear type is selected

A timer Bi interrupt request occurs when a measurement pulse’s valid edge is input or when a

counter overflow occurs. The timer Bi overflow flag is used to identify the source of the interrupt

request occurrence, that is, whether it is an overflow occurrence or a valid edge input.

The timer Bi overflow flag is set to “1” at an overflow occurrence. Accordingly, the source of the

interrupt request occurrence is identified by checking the timer Bi overflow flag in the interrupt

routine. When a value is written to the timer Bi mode register after the next count timing of the

count source with the count start bit = “1,” the timer Bi overflow flag will be cleared to “0”.

The timer Bi overflow flag is a read-only bit.

Use the timer Bi interrupt request bit to detect the overflow timing. Do not use the timer Bi overflow

flag for this detection.

s When free-run type is selected

The timer Bi overflow flag is set to “1” at an overflow occurrence. (At this time, no timer Bi interrupt

request is generated.) Accordingly, whether a counter overflow occurs between valid edges is

identified by checking the timer Bi overflow flag in the interrupt routine owing to a valid edge input.

When a value is written to the timer Bi mode register after the next count timing of the count

source with the count start bit = “1,” the timer Bi overflow flag will be cleared to “0”.

The timer Bi overflow flag is a read-only bit.

Figure 8.5.3 shows the processing example of a timer Bi interrupt when a measurement pulse’s valid

edge is detected by the timer Bi interrupt request.

8.5 Pulse period/pulse width measurement mode

Fig. 8.5.3 Processing example of timer Bi interrupt when free-run count type is selected

RTI

Timer Bi interrupt

(Note 1)

Measured value is read out.

(Note 2)

Timer Bi overflow flag ?

Timer Bi overflow flag is

cleared to “0.” (Note 3)

Processing with overflow

Processing without overflow

Notes 1: The valid edge of the measurement pulse is detected.

2: Be sure to read out the timer Bi register.

3: After the timer Bi overflow flag is set to “1”, be sure to wait for one cycle

of the count source to elapse.

Then, write a value to the timer Bi mode register.

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