HD4074344 Datasheet, PDF (33/100 Pages) Hitachi Semiconductor – 4-bit microcomputers

HD404344R Series/HD404394 Series
Active Mode: All functions operate in active mode. In active mode, the MCU is controlled by the
oscillating circuit of OSC₁ and OSC₂.
Standby Mode: The MCU switches to standby mode when an SBY instruction is executed.
In standby mode, the oscillator continues operating, but the clocks related to instruction execution stops
running. This causes the CPU to stop operating. However, the contents of RAM are retained. Also, the D
and R ports, which are set as output, maintain their status before entering standby mode. The peripheral
functions, such as interrupt, timers, serial interface, and A/D converter, continue operating.
Power dissipation in standby mode is less than in active mode because of the CPU not operating.
The MCU enters standby mode when the SBY instruction is executed in active mode.
To terminate standby mode, provide a RESET input or an interrupt request. If a reset input is given, the
MCU will be reset. If an interrupt request is given, the MCU will change to active mode and the next
instruction will be executed. After the instruction execution, if the interrupt enable flag is 1, the interrupt
operation is executed. If the interrupt enable flag is 0, normal instruction execution continues and the
interrupt request is left pending.
The standby mode flowchart is shown in figure 13.
Stop Mode: The MCU enters stop mode when a STOP instruction is received.
In stop mode, all MCU functions stop, except for maintaining RAM data. Power dissipation in this mode is
therefore the lowest of all operating modes.
In stop mode, the OSC₁ and OSC₂ oscillator is stopped.
To terminate stop mode provide either a RESET or STOPC input as shown in figure 12.
When terminating stop mode, it is important to ensure a proper oscillation stabilization period of at least t_RC
for the RESET or STOPC input. (Refer to the AC characteristics tables.)
After clearing stop mode, the RAM maintains its data kept before entering stop mode. However, the
contents of the accumulator, B register, W register, X/SPX register, Y/SPY register, carry flag, and the
serial data register are not maintained.
Clearing Stop Mode Using STOPC: The MCU is transition from stop mode to active mode by either a
RESET or STOPC input. The MCU starts instruction execution from the start of the program at address 0.
Then the RAM enable flag (RAME: $021, 3) is set accordingly, RAME = 0 for RESET input and RAME =
1 for STOPC input. A RESET input is effective when the MCU is in any mode. A STOPC input however,
is effective only in stop mode and is ignored in other modes.
So, when clearing stop mode with a STOPC input the program needs to identify the RAME status. (For
example, when the RAM contents before entering stop mode is used after transition to active mode.) A
TEST instruction for the RAM enable flag (RAME) should be executed at the beginning of the program.
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