WATCHDOG TIMER
14.2 Operation description
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.
Main routine
Watchdog timer initialized
(Value of watchdog timer :
“FFF16”) (Note 1)
Watchdog timer register
(Address 6016
8-bit dummy data
)
Watchdog timer
interrupt request occurrence
(In other words, program run-
away is detected.)
Watchdog timer interrupt routine
Software reset bit
(bit 6 at address 5E16
“1” (Note 2)
Reset microcomputer
)
RTI
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 Group User’s Manual Rev.2.0
14-6
RENESAS [ RENESAS TECHNOLOGY CORP ]
