7906 datasheet(335/531 Pages) RENESAS

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WATCHDOG TIMER

7906 Group User’s Manual Rev.2.0

14-2

14.1 Block description

The watchdog timer functions as follows:

q Detects a program runaway.

q At stop mode termination, measures a certain time after oscillation starts. (Refer to section “15.3 Stop

mode.”)

14.1 Block description

Figure 14.1.1 shows the block diagram of the watchdog timer, and registers relevant to the watchdog timer

are described below.

1/ 16

Wf32

Wf512

1/ 16

RESET

fX 16

fX 32

fX 64

fX 128

Wait mode

Divided f(XIN)

Watchdog timer clock source select

bits at STP termination

• Watchdog timer register: address 6016

• Watchdog timer frequency select bit: bit 0 at address 6116

• Watchdog timer clock source select bits at STP termination: bits 7, 6 at address 6116

❈ When the most significant bit of the watchdog timer becomes “0,” this signal will be generated.

Note: During the stop mode and until the stop mode is terminated, setting for disabling the

watchdog timer is ignored. (Refer to section “14.1.3 Particular function select register 2.”)

STP instruction

Writing to watchdog

timer register

Disables watchdog

timer (Note).

Watchdog timer

frequency select bit

Stop mode

Watchdog timer

“FFF16” is set.

❈

Watchdog timer

interrupt request

Fig. 14.1.1 Block diagram of watchdog timer

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