Processor States - Hitachi SH7751 Hardware Manual

Note: The SH7751 Series does not support endian conversion for the 64-bit data format.
Therefore, if double-precision floating-point format (64-bit) access is performed in little
endian mode, the upper and lower 32 bits will be reversed.
2.6

Processor States

The SH7751 Series has five processor states: the reset state, exception-handling state, bus-released
state, program execution state, and power-down state.
Reset State: In this state the CPU is reset. The power-on reset state is entered when the
pin goes low. The CPU enters the manual reset state if the
pin is low. For more information on resets, see section 5, Exceptions.
In the power-on reset state, the internal state of the CPU and the on-chip peripheral module
registers are initialized. In the manual reset state, the internal state of the CPU and registers of on-
chip peripheral modules other than the bus state controller (BSC) are initialized. Since the bus
state controller (BSC) is not initialized in the manual reset state, refreshing operations continue.
Refer to the register configurations in the relevant sections for further details.
Exception-Handling State: This is a transient state during which the CPU's processor state flow
is altered by a reset, general exception, or interrupt exception source.
In the case of a reset, the CPU branches to address H'A000 0000 and starts executing the user-
coded exception handling program.
In the case of a general exception or interrupt, the program counter (PC) contents are saved in the
saved program counter (SPC), the status register (SR) contents are saved in the saved status
register (SSR), and the R15 contents are saved in saved general register 15 (SGR). The CPU
branches to the start address of the user-coded exception service routine found from the sum of the
contents of the vector base address and the vector offset. See section 5, Exceptions, for more
information on resets, general exceptions, and interrupts.
Program Execution State: In this state the CPU executes program instructions in sequence.
Power-Down State: In the power-down state, CPU operation halts and power consumption is
reduced. The power-down state is entered by executing a SLEEP instruction. There are three
modes in the power-down state: sleep mode, deep sleep mode, and standby mode. For details, see
section 9, Power-Down Modes.
Bus-Released State: In this state the CPU has released the bus to a device that requested it.
Transitions between the states are shown in figure 2.6.
Rev. 3.0, 04/02, page 48 of 1064


pin is high and the