11.4.4 Switching between Watchdog Timer Mode and Interval Timer Mode
If a switch is made between watchdog timer mode and interval timer mode while the WDT is
operating, correct operation may not be performed. The WDT must be stopped (by clearing the
TME bit to 0) before changing the timer mode.
11.4.5 System Reset by RESO Signal
If the RESO output signal is input to the chip’s RES pin, the chip will not be initialized correctly.
Ensure that the RESO signal is not logically input to the chip’s RES pin. When resetting the entire
system with the RESO signal, use a circuit such as that shown in figure 11.8.
H8/3437 Series chip
Reset input
RES
Reset signal to entire chip
RESO
Figure 11.8 Sample Circuit for System Reset by RESO Signal
11.4.6 Detection of Program Runaway
The following points should be noted when using the microcomputer’s on-chip watchdog timer to
detect program runaway.
During program runaway, instructions other than the usual instructions may be executed. If an
instruction reserved for system use is executed as a result of runaway, the watchdog timer may
sometimes stop, preventing detection of the runaway.
This problem can be avoided by making the following settings in the program.
1. Set code H'0004 in ROM address H'0002.
2. Set code H'56F0 in ROM address H'0004.
As system reserved addresses may be used by an emulator, the above settings should only be made
for the actual chip.
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HITACHI [ HITACHI SEMICONDUCTOR ]
