APPENDIX
Appendix 8. 7906 Group Q & A
Watchdog timer
Q
In detection of a program runaway with usage of the watchdog timer, if the same value as that
at the reset vector address is set to the watchdog timer interrupt’s vector address, not performing
software reset, how does it occur?
When a branch is made to the branch destination address for reset within the watchdog timer
interrupt routine, how does it occur?
A
The CPU registers and the SFR are not initialized in the above-mentioned way. Accordingly,
the user must initialize all of them by software.
Note that the processor interrupt priority level (IPL) retains “7” and is not initialized. Consequently,
all interrupt requests cannot be accepted.
When rewriting the IPL by software, be sure to save the 16-bit immediate value to the stack
area, and then restore that 16-bit immediate value to all bits of the processor status register
(PS).
When a program runaway occurs, we recommend to perform software reset in order to
initialize the microcomputer.
7906 Group User’s Manual Rev.2.0
20-108
RENESAS [ RENESAS TECHNOLOGY CORP ]
