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2-35

7220 Group User’s Manual

FUNCTIONAL DESCRIPTION

2.6 Timers

2.6.1 Timer functions

There are four timers; Timer 1, Timer 2, Timer 3, Timer 4 and each timer has an 8-bit reload latch. All

timers are the count-down type, and when the timer latch value is “n”, the divide ratio is 1/(n+1)(“n” = 0

to 255). When the valve “n” is written to reload latch, is also set “n” to its timer, simultaneously.

Timer value is counted down each rising edge of count source. The timer overflows at the count next pulse,

after the count value reaches “0016,” and the interrupt request occurs. At the same time of timer overflow,

the reload latch value “n” is set (reload) to timer, and timer continues to count down. The divide ratio is

1/(n+1). Make sure that set “n” in the range “0016” to “FF16.”

Count source

Timer

Overflow signal

Interrupt request

Writing Value

nn16

nn16-1

0016

0116

nn16-1

nn16

Fig. 2.6.2 Timer overflow timing

(1)

Timer 1

Timer 1 can select one of the following count sources:

q f(XIN)/16

q f(XIN)/4096

(This is a clock by f(XIN)/4096 interrupt and is valid only when PWM count source is supplied.)

The count source of timer 1 is selected by setting bit 0 of the timer 12 mode register (address

00F416).

Timer 1 interrupt request occurs at timer 1 overflow.

(2)

Timer 2

Timer 2 can select one of the following count sources:

q f(XIN)/16

q Timer 1 overflow signal

q External clock from pin P24/TIM2

The count source of timer 2 is selected by setting bits 4 and 1 of the timer 12 mode register (address

00F416). When timer 1 overflow signal is a count source for timer 2, timer 1 functions as an 8-bit

prescaler.

Timer 2 interrupt request occurs at timer 2 overflow.

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