7480 datasheet(115/337 Pages) RENESAS

115 / 337 page

7480 Group and 7481 Group User's Manual

1-98

HARDWARE

1.13 Timer 1 and Timer 2

1.13.3 Basic Operations of Timer 1 and Timer 2

Basic operations of timer 1 and timer 2 are described below.

For details, refer to (1) Operations of each mode.

Count Sources

Timer 1 and timer 2 can select the following count sources with the timer 1 or 2 count source select bits

of the timer 1 or 2 mode register:

• f(XIN)/8

• f(XIN)/64

• f(XIN)/128

• f(XIN)/256

Writes to Timers

When ‘TL(0016 through FF16)’ is written to a timer, ‘TL’ is set in both the timer and the timer latch.

Note: A write to an operating timer causes the contents of the timer to be affected, so that the period from

the last underflow until the next underflow is undefined.

Reads from Timers

The contents of the timer can be read by a read operation.

Count Operations

The count operation (start/stop) of timer 1 or timer 2 is controlled by the timer 1 or 2 stop control bit of

the timer 1 or 2 mode register as follows:

• When the timer 1 or 2 stop control bit is set to ‘0’, the timer starts counting.

• When the timer 1 or 2 stop control bit is set to ‘1’, the timer stops counting.

In the count operation, the contents of each timer are decremented by 1 at every rising edge of the count

source.

The timer 1 or 2 stop control bit is recognized during the HIGH time of the count source. When the count

has stopped, the count source cannot be accepted.

Reloading Timers

When a timer reaches ‘FF16’ in the count operation, an underflow occurs at the subsequent rising edge of

the count source, and the value decremented by 1 from the contents of the timer latch is reloaded to the

timer.

Timer Interrupt

At an underflow, the timer 1 or 2 interrupt request bit of interrupt request register 1 is set to ‘1’; then a

timer interrupt request is generated.

Table 1.13.1 lists the relation between timer count periods and values set to timer 1 and timer 2.

7480 Datasheet(PDF) 115 Page - Renesas Technology Corp