M38C89MB datasheet(24/55 Pages) RENESAS

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SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER

MITSUBISHI MICROCOMPUTERS

38C8 Group

Timer 1, Timer 2, Timer 3

Timer 1, timer 2, and timer 3 are 8-bit timers. The count source for

each timer can be selected by the timer 123 mode register. The timer

latch value is not affected by a change of the count source. However,

because changing the count source may cause an inadvertent count

down of the timer. Therefore, rewrite the value of timer whenever the

count source is changed.

qTimer 2 write control

If the timer 2 write control bit is “0”, when the value is written in the

address of timer 2, the value is loaded in the timer 2 and the latch at

the same time.

If the timer 2 write control bit is “1”, when the value is written in the

address of timer 2, the value is loaded only in the latch. The value in

the latch is loaded in timer 2 after timer 2 underflows.

sNotes on timer 1 to timer 3

When the count source of timer 1 to 3 is changed, the timer counting

value may be changed large because a thin pulse is generated in

count input of timer. If timer 1 output is selected as the count source

of timer 2 or timer 3, when timer 1 is written, the counting value of

timer 2 or timer 3 may be changed large because a thin pulse is

generated in timer 1 output.

Therefore, set the value of timer in the order of timer 1, timer 2 and

timer 3 after the count source selection of timer 1 to 3.

Fig. 19 Structure of timer 123 mode register

Timer 123 mode register

(T123M :address 002916)

* Internal clock

φ is XCIN/2 in the low-speed mode.

Timer 1 count source selection bit

0 : f(XIN)/16

(or f(XCIN)/16 in low-speed mode*)

1 : f(XCIN)/32

Not used

Timer 2 write control bit

0 : Write data in latch and counter

1 : Write data in latch only

Timer 2 count source selection bit

0 : Timer 1 output

1 : f(XIN)/16

(or f(XCIN)/16 in low-speed mode*)

Timer 3 count source selection bit

0 : Timer 1 output

1 : f(XCIN)/32

Not used (return “0” when read)

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