Reset Operation - Fujitsu 8FX Hardware Manual

CHAPTER 4 RESET

4.1 Reset Operation

4.1 Reset Operation
When a reset source occurs, the CPU immediately stops the process being
executed and enters the reset release wait state. When the reset is released,
the CPU reads mode data and the reset vector from the Flash memory (mode
fetch). When the power is switched on or when the device is released from a
reset in subclock mode, sub-CR clock mode, or stop mode, the CPU performs
mode fetch after the oscillation stabilization wait time has elapsed.
■ Reset Sources
There are five reset sources for the reset.
Table 4.1-1 Reset Sources
Reset source
External reset
Software reset
Watchdog reset
Power-on reset
Low-voltage detection reset (optional)
● External reset
An external reset is generated if "L" level is input to the external reset pin (RST).
An external input reset signal is received asynchronously with the operating clock of the
microcontroller via the internal noise filter and then generates an internal reset signal that is
synchronized with the machine clock to initialize the internal circuit. Therefore, the operating
clock of the microcontroller is necessary for initializing the internal circuit. In order to operate
with the external clock, external clock signals must be input. However, the external pins
(including I/O ports and peripheral functions) are reset asynchronously. In addition, there is a
standard value of the pulse width for external reset input. If the value is below the standard
value, a reset signal may not be accepted.
The standard value is shown in the device data sheet. Design an external reset circuit that
satisfies the standard value.
● Software reset
Writing "1" to the software reset bit of the standby control register (STBC:SRST) generates a
software reset.
● Watchdog reset
After the watchdog timer starts, a watchdog reset is generated if the watchdog timer is not
cleared within a predetermined period of time.
● Power-on reset
A power-on reset is generated when the power is switched on.
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"L" level is input to the external reset pin.
"1" is written to the software reset bit in the standby control register
(STBC:SRST).
The watchdog timer overflows.
The power is switched on.
The supply voltage falls below the detection voltage.
FUJITSU SEMICONDUCTOR LIMITED
MB95630H Series
Reset condition
MN702-00009-2v0-E