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4.2
Reset
4.2.1
Overview
A reset has the highest exception priority.
When the
RES or MRES pin goes low, all processing halts and the H8S/2214 enters the reset state.
A reset initializes the internal state of the CPU and the registers of on-chip supporting modules.
Immediately after a reset, interrupt control mode 0 is set.
Reset exception handling begins when the
RES or MRES pin changes from low to high.
The levels of the
RES and MRES pins at reset determine whether a power-on reset or a manual
reset is effected.
The H8S/2214 can also be reset by overflow of the watchdog timer. For details see section 11,
Watchdog Timer.
4.2.2
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 supporting modules, while a manual reset initializes all the registers
in the on-chip supporting modules except for the bus controller and I/O ports, which retain their
previous states.
With a manual reset, since the on-chip supporting modules are initialized, ports used as on-chip
supporting module I/O pins are switched to I/O ports controlled by DDR and DR.
Table 4-3
Reset Types
Reset Transition
Conditions
Internal State
Type
MRES
RES
CPU
On-Chip Supporting Modules
Power-on reset
*
Low
Initialized
Manual reset
Low
High
Initialized
Initialized, except for bus controller
and I/O ports
*: Don’t care