3822 datasheet(104/328 Pages) RENESAS

104 / 328 page

APPLICATION

2.3 Timer X and timer Y

3822 GROUP USER’S MANUAL

2–38

(4) Pulse width measurement mode

In the pulse width measurement mode, the width (“H” or “L” level) of a pulse input from the P54/CNTR0

pin is measured.

Operation in the pulse width measurement mode is described below.

Count operation

Immediately after reset, the timer X stop control bit is in the “0” state. In this state, a count operation

is continued in the period in which the measurement level is input to the P54/CNTR0 pin.

The value of the X counter is decremented by 1 each time a count source is input.

The count source is f(XIN)/16 clock (low-speed mode ; f(XCIN)/16 clock).

Reload operation

The X counter underflows at the first count pulse after the value of the X counter reaches “0016.”

At this time, the value of the X latch is transferred (reloaded) to the X counter.

Pulse width measurement

As a pulse measurement period, a “H” or “L” is selected by the CNTR0 active edge switch bit.

The difference between the initial value of the X counter and the X counter value at counter stop

is a measured pulse width.

A reload operation by reading the count value is not performed automatically. Accordingly, to

continue the measurement, set the initial value anew by software.

Interrupt operation

sEdge of pulse measured

At the edge of the pulse input from the P54/CNTR0 pin, an interrupt request occurs. At the same

time, the CNTR0 interrupt request bit is set to “1.” The occurrence of an interrupt is controlled by

the CNTR0 interrupt enable bit.

The CNTR0 active edge switch bit specifies an active edge. When “H” level width is measured, the

falling edge (

) is active, when “L” level width is measured, the rising edge (

) is active.

sCounter underflow

An interrupt request occurs at the X counter underflow. At the same time, the timer X interrupt

request bit is set to “1.” The occurrence of an interrupt is controlled by using the timer X interrupt

enable bit.

Figure 2.3.4 shows a pulse width measurement mode operation example.

3822 Datasheet(PDF) 104 Page - Renesas Technology Corp