7906 datasheet(174/531 Pages) RENESAS

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7906 Group User’s Manual Rev.2.0

8-23

TIMER B

8.5 Pulse period/pulse width measurement mode

8.5.2 Operation in pulse period/pulse width measurement mode

s When counter clear type is selected

➀ When the count start bit is set to “1,” the counter starts counting of the count source.

➁ The counter value is transferred to the reload register when a valid edge of the measurement pulse

is detected. (Refer to section “(1) Pulse period/Pulse width measurement.”)

➂ The counter value is cleared to “000016” after the transfer in ➁, and the counter continues counting.

➃ The timer Bi interrupt request bit is set to “1” when the counter value is cleared to “000016” in ➂ (Note).

The interrupt request bit remains set to “1” until the interrupt request is accepted or until the interrupt

request bit is cleared to “0” by software.

➄ The timer repeats operations ➁ to ➃ above.

Note: No timer Bi interrupt request occurs when the first valid edge is input after the counter starts counting.

s When free-run type is selected

➀ When the count start bit is set to “1,” the counter starts counting of the count source.

➁ The counter value is transferred to the reload register when a valid edge of the measurement pulse

is detected. (Refer to section “(1) Pulse period/Pulse width measurement.”)

➂ The timer Bi interrupt request bit is set to “1” after the transfer in ➁ (Note).

The interrupt request bit remains set to “1” until the interrupt request is accepted or until the interrupt

request bit is cleared to “0” by software.

The counter continues counting with the counter value kept.

➃ When a counter overflow occurs, the timer Bi overflow flag is set to “1,” and counting continues after

clearing the counter value to “000016 .” At this time, the timer Bi interrupt request bit does not change.

➄ The timer repeats operations ➁ to ➃ above.

Note: No timer Bi interrupt request occurs when the first valid edge is input after the counter starts counting.

(1)

Pulse period/pulse width measurement

The measurement mode select bits (bits 3 and 2 at addresses 5B16 and 5D16) specify whether the

pulse period of an external signal is measured or its pulse width is done. Table 8.5.3 lists the

relationship between the measurement mode select bits and the pulse period/pulse width measurements.

Make sure that the measurement pulse interval from the falling edge to the rising edge, and vice

versa are two cycles of the count source or more. Additionally, use software to identify whether the

measurement result indicates the “H” level width or the “L” level width.

Table 8.5.3 Relationship between measurement mode select bits and pulse period/pulse width measurements

Pulse period/Pulse width measurement

Pulse period measurement

Pulse width measurement

Measurement interval (Valid edges)

From falling edge to falling edge (Falling edges)

From rising edge to rising edge (Rising edges)

From falling edge to rising edge, and vice versa

(Falling and rising edges)

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