Rev. 3.0, 10/02, page 67 of 686
4.3
Reset
A reset has the highest exception priority.
When the
RES
or
MRES
pin goes low, all processing halts and this LSI enters the reset state. To
ensure that this LSI is reset, hold the
RES
or
MRES
pin low for at least 20 ms at power-up or hold
the
RES
or
MRES
pin low for at least 20 states during operation.
A reset initializes the internal state of the CPU and the registers of on-chip peripheral modules.
This LSI can also be reset by overflow of the watchdog timer. For details, see section 12,
Watchdog Timer.
Immediately after a reset, interrupt control mode 0 is set.
4.3.1
Reset Types
A reset can be of either of two types: a power-on reset or a manual reset. Reset types are shown in
table 4.3. A power-on reset should be used when powering on.
The internal state of the CPU is initialized by either type of reset. A power-on reset also initializes
all the registers in the on-chip peripheral modules, while a manual reset initializes all the registers
in the on-chip peripheral modules except for the bus controller and I/O ports, which retain their
previous states.
With a manual reset, since the on-chip peripheral modules are initialized, ports used as on-chip
peripheral module I/O pins are switched to I/O ports controlled by DDR and DR.
Table 4.3
Reset Types
Reset Transition
Condition
Internal State
Type
MRES
MRES
MRES
MRES
RES
RES
RES
RES
CPU
On-Chip Peripheral Modules
Power-on reset
*
Low
Initialized
Initialized
Manual reset
Low
High
Initialized
Initialized, except for bus controller and I/O
ports
Note:
*
Don’t care
A reset caused by the watchdog timer can also be of either of two types: a power-on reset or a
manual reset.
When the
MRES
pin is used,
MRES
pin input must be enabled by setting the MRESE bit to 1 in
SYSCR.
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