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Rev. 1.00, 05/04, page 46 of 544
2.8 Processing States
The H8S/2000 CPU has four main processing states: the reset state, exception handling state,
program execution state, and program stop state. Figure 2.13 indicates the state transitions.
• Reset state
In this state the CPU and on-chip peripheral modules are all initialized and stopped. When the
RES input goes low, all current processing stops and the CPU enters the reset state. All
interrupts are masked in the reset state. Reset exception handling starts when the RES signal
changes from low to high. For details, refer to section 4, Exception Handling.
The reset state can also be entered by a watchdog timer overflow.
• Exception-handling state
The exception-handling state is a transient state that occurs when the CPU alters the normal
processing flow due to an exception source, such as, a reset, trace, interrupt, or trap instruction.
The CPU fetches a start address (vector) from the exception vector table and branches to that
address. For further details, refer to section 4, Exception Handling.
• Program execution state
In this state the CPU executes program instructions in sequence.
• Program stop state
This is a power-down state in which the CPU stops operating. The program stop state occurs
when a SLEEP instruction is executed or the CPU enters hardware standby mode. For details,
refer to section 20, Power-Down Modes.