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WATCHDOG TIMER

7721 Group User’s Manual

15–3

15.1.1 Watchdog timer

Watchdog timer is a 12-bit counter where the count source which is selected with the watchdog timer

frequency select bit (bit 0 at address 6116) is counted down. A value “FFF16” is automatically set in

Watchdog timer in the cases listed below. An arbitrary value cannot be set to Watchdog timer.

q When dummy data is written to the watchdog timer register (Refer to “Figure 15.1.2.”)

q When the most significant bit of Watchdog timer becomes “0”

q When the STP instruction is executed (Refer to section “5.3 Stop mode.”)

q At reset

15.1 Block description

Fig. 15.1.2 Structure of watchdog timer register

15.1.2 Watchdog timer frequency select register

This is used to select a Watchdog timer’s count source. Figure 15.1.3 shows the structure of the watchdog

timer frequency select register.

Fig. 15.1.3 Structure of watchdog timer frequency select register

Watchdog timer register (Address 6016)

Bit

Initializes Watchdog timer.

When dummy data is written to this register, Watchdog

timer’s value is initialized to “FFF16.” (Dummy data: 0016 to FF16)

At reset

Undefined

Functions

7 to 0

–

0 : f512

1 : f32

At reset

Undefined

Functions

Watchdog timer frequency select register (Address 6116)

Bit

Nothing is assigned.

Watchdog timer frequency select

bit

Bit name

7 to 1

–

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