m37905 Renesas Electronics Corporation., m37905 Datasheet - Page 363

• Manufacturer Part Number: m37905
• Description: Mitsubishi 16-bit Single-chip Microcomputer 7700 Family / 7900 Series
• Manufacturer: Renesas Electronics Corporation.

Fig. 14.2.1 Example of program runaway detection by watchdog timer
WATCHDOG TIMER
14.2 Operation description
14-6
Be sure to write dummy data to the watchdog timer register (address 60
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 5E
Figure 14.2.1 shows an example of a program runaway detected by the watchdog timer.
Watchdog timer
interrupt request occurrence
(In other words, program run-
Notes 1: Be sure to initialize the watchdog timer before the most significant bit of the
away is detected.)
2: When a program runaway occurs, values of the data bank register (DT), direct
watchdog timer becomes “0.” (In other words, be sure to write dummy data to
address 60
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.
Watchdog timer register
(Address 60
Software reset bit
(bit 6 at address 5E
16
16
) in the watchdog timer interrupt routine.
Watchdog timer interrupt routine
before a watchdog timer interrupt request occurs).
16
)
7905 Group User’s Manual Rev.1.0
Main routine
16
RTI
)
“1” (Note 2)
8-bit dummy data
Reset microcomputer
Watchdog timer initialized
(Value of watchdog timer :
“FFF
16
) before the most significant bit
16
”) (Note 1)