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7. CPU Operating States
The H8/300L CPU operates in four states, namely, program execution state, program halt state,
exception handling state, and reset state. The figure below shows the transitions between these
states.
State Transition Diagram
Reset state
Reset request
Program halt state
Reset State: The H8/300L CPU is reset in this state.
Program Execution State: In this state the H8/300L CPU executes instructions sequentially.
The program execution state has two modes: active mode and subactive mode. In active mode
the CPU operates on the system clock and in subactive mode the CPU operates according to
the subclock. (For further details see the section titled "Low Power Modes" later in this
document.)
Exception Handling State: This is a transient state that occurs when the H8/300L CPU
execution state flow is changed by a reset, interrupt, or exception. The program counter and
condition code register are saved on the stack using the stack pointer.
Program Halt State: The program halt state has three modes: sleep mode, standby mode, and
watch mode. (For further details see the "Low Power Modes" section later in this document.)
Reset release
Reset request
Interrupt request
SLEEP instruction execution
45
Exception handling state
Interrupt
request
Reset request
Program execution state
CPU
Exception
handling
completion
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