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CLOCK GENERATING CIRCUIT

7906 Group User’s Manual Rev.2.0

4-10

(1) External clock input select bit (bit 1)

When this bit is “0,” the oscillation driver circuit between pins XIN and XOUT operates. At the stop mode

termination owing to an interrupt request occurrence, the watching timer is used.

Setting this bit to “1” stops the oscillation driver circuit between pins XIN and XOUT and keeps the output

level at pin XOUT being “H.” (Refer to section “16.3 Stop of oscillation circuit.”) At the stop mode

termination owing to an interrupt request occurrence, the watchdog timer is not used if the system

clock select bit (bit 5 at address BC16) = “0,” where as the watchdog timer is used if the system clock

select bit = “1.”

To rewrite this bit, write “0” or “1” just after writing of “5516” to address 6216. (See Figure 4.2.5.)

Note that if an interrupt occurs between writing of “5516” and next writing of “0” or “1,” latter writing

may be ignored. When there is a possibility that an interrupt occurs at the above timing, be sure to

read this bit’s contents after writing of “0” or “1,” and verify whether “0” or “1” has correctly been

written or not.

In addition, even when the watchdog timer is disabled by the particular function select register 2

(address 6416), the watchdog timer can be active only at the stop mode termination if this bit = “0.”

(Refer to section “15.3 Stop mode.”)

4.2 Clocks

Fig. 4.2.5 Writing procedure for particular function select register 0

Writing of “5516”

Particular function select register 0 (Address 6216)

Setting completed

Writing to bits 0, 1

Particular function select register 0 (Address 6216)

External clock input select bit

0 : Oscillation circuit is active. (Oscillator is connected.)

Watchdog timer is used at stop mode termination.

1 : Oscillation circuit is inactive. (External clock is input.)

When the system clock select bit (bit 5 at address BC16) = “0,”

watchdog timer is not used at stop mode termination.

When the system clock select bit = “1,”

watchdog timer is used at stop mode termination.

STP instruction invalidity select bit

0 : STP instruction is valid.

1 : STP instruction is invalid.

instruction

Note: Bits’ state does not change only

by writing of “5516.”

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