CHAPTER 21 RESET FUNCTION
21.1 Reset Function
The reset signal can be effected by the following two methods:
(1) External reset input from RESET pin
(2) Internal reset by inadvertent loop time detection by watchdog timer
There is no functional difference between the external reset and internal reset, and execution of the program is
started from addresses written to addresses 0000H and 0001H when the RESET signal is input.
The reset function is effected when a low-level signal is input to the RESET pin or when an overflow occurs in
the watchdog timer. As a result, each hardware enters the status shown in Table 21-1. Each pin goes into a high-
impedance state while the RESET signal is input, and during the oscillation stabilization time immediately after the
reset function has been released.
When a high-level signal is input to the RESET pin, the reset function is released, and program execution is started
after oscillation stabilization time (2
18
/f
X
) has elapsed. The reset function effected by an overflow in the watchdog
timer is automatically released after reset, and program execution is started after the oscillation stabilization time (2
18
/
f
X
) has elapsed (refer to
Figures 21-2
through
21-4
).
Cautions 1. Input a low-level signal to the RESET pin for 10
μ
s or longer to execute external reset.
2. Oscillation of the main system clock is stopped while the RESET signal is input. Oscillation
of the subsystem clock is not stopped but continues.
3. To release the STOP mode by the RESET input, the contents in the STOP mode are retained
while the RESET signal is input. However, the port pins go into a high-impedance state.
Figure 21-1. Block Diagram of Reset Function
Reset
control circuit
Watchdog timer
RESET
Count clock
Stops
Overflow
Reset
signal
Interrupt
function
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