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3.4.3
Exception Handling State
The exception handling state is the transitional state in which the HMCS400 CPU normal
processing flow has changed due to a reset, the clearing of stop mode, or an interrupt. In interrupt
exception handling, the program counter (PC), carry (CA), and status (ST) are saved on the stack.
Refer to section 4, “Exception Handling”, for details on exception handling.
3.4.4
Program Stopped State
The program stopped state has three modes: stop mode, watch mode, and standby modes. These
modes realize low power states.
(1) Stop Mode: Stop mode is entered when a STOP instruction is executed in active mode when
the TMA3 bit in timer mode register A (TMA) is set to 0.
The system clock oscillator stops and the CPU, peripheral functions, and I/O ports go to the reset
state. The contents of RAM will be maintained as long as the stipulated voltage is applied.
The transition to stop mode must be made from active mode.
(2) Watch Mode (HD404339/HD404369 Series Products Only): Watch mode is entered in the
following two cases:
A STOP instruction is executed in active mode with the TMA3 bit in timer mode register A
(TMA) set to 1, or
Either a STOP or SBY instruction is executed in subactive mode with either the LSON flag set
to 1 (and the DTON flag either 0 or 1) or both the LSON flag set to 0 and the DTON flag set to
0.
The system clock oscillator stops but the subsystem clock oscillator continues to operate.
Although the CPU and the built-in peripheral modules stop, the contents of RAM, the CPU
registers, and the peripheral function registers are maintained as long as the stipulated voltage is
applied. The I/O port states are also maintained. However, note that of the built-in peripheral
modules, timer A continues to operate.
(3) Standby Mode: Standby mode is entered when an SBY instruction is executed. (active mode
→ standby mode)
Although operating clock supply to the CPU is stopped and the CPU stops, the built-in peripheral
functions continue to operate. The contents of the CPU registers and RAM and the I/O port states
are maintained.