Reset Sources; Initialization Conditions (Reset Groups) - Epson S1C17M20 Technical Manual

2.2.3 Reset Sources

The reset source refers to causes that request system initialization. The following shows the reset sources.
#RESET pin
Inputting a reset signal with a certain low level period to the #RESET pin issues a reset request.
POR and BOR
POR (Power On Reset) issues a reset request when the rise of V
a reset request when a certain V
system will be reset properly when the power is turned on and the supply voltage is out of the operating voltage
range. Figure 2.2.3.1 shows an example of POR and BOR internal reset operation according to variations in V
V
DD
V
SS
Internal state
X RST
V : Reset detection voltage V
RST-
For the POR and BOR electrical specifications, refer to "POR/BOR characteristics" in the "Electrical Charac-
teristics" chapter.
Key-entry reset
Inputting a low level signal of a certain period to the I/O port pins configured to a reset input issues a reset re-
quest. This function must be enabled using an I/O port register. For more information, refer to the "I/O Ports"
chapter.
Watchdog timer reset
Setting the watchdog timer into reset mode will issue a reset request when the counter overflows. This helps re-
turn the runaway CPU to a normal operating state. For more information, refer to the "Watchdog timer" chapter.
Supply voltage detector reset
By enabling the low power supply voltage detection reset function, the supply voltage detector will issue a reset
request when a drop in the power supply voltage is detected. This makes it possible to put the system into reset
state if the IC must be stopped under a low voltage condition. For more information, refer to the "Supply Volt-
age Detector" chapter.
Peripheral circuit software reset
Some peripheral circuits provide a control bit for software reset (MODEN or SFTRST). Setting this bit initial-
izes the peripheral circuit control bits. Note, however, that the software reset operations depend on the periph-
eral circuit. For more information, refer to "Control Registers" in each peripheral circuit chapter.
Note: The MODEN bit of some peripheral circuits does not issue software reset.

2.2.4 Initialization Conditions (Reset Groups)

A different initialization condition is set for the CPU registers and peripheral circuit control bits, individually. The
reset group refers to an initialization condition. Initialization is performed when a reset source included in a reset
group issues a reset request. Table 2.2.4.1 lists the reset groups. For the reset group to initialize the registers and con-
trol bits, refer to the "CPU and Debugger" chapter or "Control Registers" in each peripheral circuit chapter.
S1C17M20/M21/M22/M23/M24/M25
TECHNICAL MANUAL (Rev. 1.0)
voltage level is detected. Reset requests from these circuits ensure that the
DD
V
RST+
V V
RST- RST-
RUN RST
Reset canceling voltage
RST+:
Figure 2.2.3.1 Example of Internal Reset by POR and BOR
Seiko Epson Corporation
2 POWER SUPPLY, RESET, AND CLOCKS
is detected. BOR (Brownout Reset) issues
DD
V
RST-
RUN RST X
Indefinite (operating limit)
X RST
DD
V
RST+
RST RUN X
RESET state CPU RUN state
RUN
2-3
.