HD6413308 Hitachi Semiconductor, HD6413308 Datasheet - Page 268

• Manufacturer Part Number: HD6413308
• Description: Hitachi Single-Chip MicroComputer
• Manufacturer: Hitachi Semiconductor

14.5 Hardware Standby Mode
14.5.1 Transition to Hardware Standby Mode
Regardless of its current state, the chip enters the hardware standby mode whenever the STBY pin
goes Low.
The hardware standby mode reduces power consumption drastically by halting the CPU, stopping
all the functions of the on-chip supporting modules, and placing I/O ports in the high-impedance
state. The registers of the on-chip supporting modules are reset to their initial values. Only the on-
chip RAM is held unchanged, provided the minimum necessary voltage supply is maintained (at
least 2V).
Notes:
1.
2.
14.5.2 Recovery from Hardware Standby Mode
Recovery from the hardware standby mode requires inputs at both the STBY and RES pins.
When the STBY pin goes High, the clock oscillator begins running. The RES pin should be Low at
this time and should be held Low long enough for the clock to stabilize. When the RES pin
changes from Low to High, the reset sequence is executed and the chip returns to the program
execution state.
The RAME bit in the system control register should be cleared to “0” before the STBY pin
goes Low, to disable the on-chip RAM during the hardware standby mode.
Do not change the inputs at the mode pins (MD1, MD0) during hardware standby mode. Be
particularly careful not to let both mode pins go Low in hardware standby mode, since that
places the chip in PROM mode and increases current dissipation.
Note that the H8/300 CPU pre-fetches instructions. If an instruction stored in the last two bytes
of on-chip ROM is executed (at addresses H'3FFE and H'3FFF in the H8/330), the contents of
the next two bytes (H'4000 and H'4001), which are not in on-chip ROM, will be fetched as the
next instruction.
This problem does not occur in expanded mode when on-chip ROM is disabled (mode 1). In
hardware standby mode there is no such additional current dissipation, regardless of the
conditions when hardware standby mode is entered.
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