
46
Reset State:
The CPU resets in the reset state. This occurs when the
RES
pin level goes low.
When the NMI pin is high, the result is a power-on reset; when it is low, a manual reset will occur.
Exception Handling State
: The exception handling state is a transient state that occurs when an
exception handling source such as a reset or interrupt alters the CPU’s processing state flow.
For a reset, the initial values of the program counter (PC) (execution start address) and stack
pointer (SP) are fetched from the exception vector table and stored; the CPU then branches to the
execution start address and execution of the program begins.
For an interrupt, the stack pointer (SP) is accessed and the program counter (PC) and status
register (SR) are saved to the stack area. The exception service routine start address is fetched
from the exception processing vector table; the CPU then branches to that address and the program
starts executing, thereby entering the program execution state.
Program Execution State
: In the program execution state, the CPU sequentially executes the
program.
Power-Down State
: In the power-down state, the CPU operation halts and power consumption
declines. The SLEEP instruction places the CPU in the power-down state. This state has two
modes: sleep mode and standby mode. See section 2.5.2 for more details.
Bus-Released State
: In the bus-released state, the CPU releases the bus to the device that has
requested it.
2.5.2
Power-Down State
Besides the ordinary program execution states, the CPU also has a power-down state in which
CPU operation halts, lowering power consumption (table 2.19). There are two power-down state
modes, sleep mode and standby mode, and also a module standby function.
Sleep Mode
: When standby bit SBY (in the standby control register SBYCR) is cleared to 0 and a
SLEEP instruction executed, the CPU moves from program execution state to sleep mode. The on-
chip peripheral modules other than the CPU do not halt in the sleep mode. To return from sleep
mode, use a reset, any interrupt, or a DMA address error; the CPU returns to the ordinary program
execution state through the exception handling state.
Software Standby Mode
: To enter the standby mode, set the standby bit SBY (in the standby
control register SBYCR) to 1 and execute a SLEEP instruction. In standby mode, all CPU, on-chip
peripheral module, and oscillator functions are halted. When entering the standby mode, confirm
that the DMAC master enable bit is 0. If a multiply instruction is in progress on entry to standby
mode, the MACL and MACH registers will be invalid. CPU internal register contents and on-chip
RAM data are retained. Cache (and on-chip RAM) data is not retained.