5 iniTial ReSeT
5-2
Seiko epson Corporation
S1C17624/604/622/602/621 TeChniCal Manual
Resetting by the Watchdog Timer
5.1.3
The S1C17624/604/622/602/621 has a built-in watchdog timer to detect runaway of the CPU. The watchdog timer
overflows if it is not reset with software (due to CPU runaway) in four-second cycles. The overflow signal can gen-
erate either NMI or reset. Write 1 to the WDTMD/WDT_ST register to generate reset (NMI occurs when WDTMD
= 0).
For details of the watchdog timer, see the “Watchdog Timer (WDT)” chapter.
notes: • When using the reset function of the watchdog timer, program the watchdog timer so that it
will be reset within four-second cycles to avoid occurrence of an unnecessary reset.
• The reset function of the watchdog timer cannot be used for power-on reset as it must be en-
abled with software.
initial Reset Sequence
5.2
Even if the #RESET pin input negates the reset signal after power is turned on, the CPU cannot boot up until the
oscillation stabilization waiting time (64 / IOSC clock frequency) has elapsed.
Figure 5.2.1 shows the operating sequence following cancellation of initial reset.
The CPU starts operating in synchronization with the IOSC (internal oscillator) clock after reset state is canceled.
note: The oscillation stabilization time described in this section does not include oscillation start time.
Therefore the time interval until the CPU starts executing instructions after power is turned on or
SLEEP mode is canceled may be longer than that indicated in the figure below.
Boot vector
Oscillation stabilization
waiting time
Booting
IOSC clock
#RESET
Internal reset
Internal data request
Internal data address
Internal reset canceled
Reset canceled
2.1 Operation Sequence Following Cancellation of Initial Reset
Figure 5.
initial Settings after an initial Reset
5.3
The CPU internal registers are initialized as follows at initial reset.
R0–R7: 0x0
PSR:
0x0 (interrupt level = 0, interrupt disabled)
SP:
0x0
PC:
Reset vector stored at the beginning of the vector table is loaded by the reset handling.
The internal RAM and display memory should be initialized with software as they are not initialized at initial reset.
The internal peripheral modules are initialized to the default values (except some undefined registers). Change the
settings with software if necessary. For the default values set at initial reset, see the list of I/O registers in Appendix
or descriptions for each peripheral module.