Filter
Top Products
Rev. 1.00, 05/04, page 61 of 544
4.3 Reset
A reset has the highest exception priority. When the RES pin goes low, all processing halts and
this LSI enters the reset. To ensure that this LSI is reset, hold the RES pin low for at least 20 ms at
power-on. To reset the chip during operation, hold the RES pin low for at least 20 states. A reset
initializes the internal state of the CPU and the registers of on-chip peripheral modules. The chip
can also be reset by overflow of the watchdog timer. For details, see section 11, Watchdog Timer
(WDT).
4.3.1 Reset Exception Handling
When the RES pin goes high after being held low for the necessary time, this LSI starts reset
exception handling as follows:
1. The internal state of the CPU and the registers of the on-chip peripheral modules are initialized
and the I bit is set to 1 in CCR.
2. The reset exception handling vector address is read and transferred to the PC, and program
execution starts from the address indicated by the PC.
Figure 4.1 shows an example of the reset sequence.
φ
RES
Internal address bus
Internal read signal
Internal write signal
Internal data bus
Vector
fetch
(1) Reset exception handling vector address ((1) = H'0000)
(2) Start address (contents of reset exception handling vector address)
(3) Start address ((3) = (2))
(4) First program instruction
(1) (3)
High
Internal
processing
Prefetch of first program
instruction
(2) (4)
Figure 4.1 Reset Sequence (Mode 3)