7906 datasheet(339/531 Pages) RENESAS

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WATCHDOG TIMER

7906 Group User’s Manual Rev.2.0

14-6

Be sure to write dummy data to the watchdog timer register (address 6016) before the most significant bit

of the watchdog timer becomes “0.” When writing to the watchdog timer is not performed owing to a

program runaway and the watchdog timer’s most significant bit becomes “0,” a watchdog timer interrupt

request occurs. This informs that a program runaway has occurred.

In order to reset the microcomputer when a program runaway has been detected, write “1” to the software

reset bit (bit 6 at address 5E16) in the watchdog timer interrupt routine.

Figure 14.2.1 shows an example of a program runaway detected by the watchdog timer.

14.2 Operation description

RTI

Main routine

Watchdog timer interrupt routine

Watchdog timer register

(Address 6016)

8-bit dummy data

Watchdog timer

interrupt request occurrence

(In other words, program run-

away is detected.)

Watchdog timer initialized

(Value of watchdog timer :

“FFF16”) (Note 1)

Software reset bit

(bit 6 at address 5E16)

“1” (Note 2)

Reset microcomputer

Notes 1: Be sure to initialize the watchdog timer before the most significant bit of the

watchdog timer becomes “0.” (In other words, be sure to write dummy data to

address 6016 before a watchdog timer interrupt request occurs).

2: When a program runaway occurs, values of the data bank register (DT), direct

page register (DPRi), etc., may be changed. When “1” is written to the software

reset bit by an addressing mode using DT, DPRi, etc., be sure to set values to

DT and DPRi, etc. again.

Fig. 14.2.1 Example of program runaway detection by watchdog timer

7906 Datasheet(PDF) 339 Page - Renesas Technology Corp