38C3 datasheet(141/224 Pages) RENESAS

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2-76

38C3 Group User’s Manual

APPLICATION

2.8 Clock generating circuit

(2)

Counting without clock error during power failure

Outline: It keeps counting without clock error during a power failure.

Specifications: •Reducing power consumption as low as possible while maintaining clock function

•Clock: f(XIN) = 4.19 MHz

•Sub clock: f(XCIN) = 32.768 kHz

•Use of Timer 3 interrupt

For the peripheral circuit and the status transition during a power failure, refer to “Figures 2.8.2 and

2.8.3”.

Figure 2.8.6 shows the structure of clock counter, Figures 2.8.7 and 2.8.8 show the setting of

relevant registers.

Fig. 2.8.6 Structure of clock counter

When the system returns from a

power failure, add the time taken

for the switching processing for the

return.

Timer 1 interrupt

1/256

Timer 2Timer 3

244

µs

1/16

f(XCIN) = 32.768 kHz

1/8

Timer 1

f(XIN) = 4.19 MHz

Timer 1Base counter1 second counter1 minute counter

1/16

1/641/256

1/16

1/60

1 second

Minute/Time/Day/

Month/Year

244

µs

Timer 3 interrupt

: Software timer

: Hardware timer

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