HD6433044 Hitachi Semiconductor, HD6433044 Datasheet - Page 65

• Manufacturer Part Number: HD6433044
• Description: (HD64 Series) Hitachi Single-Chip Microcomputer
• Manufacturer: Hitachi Semiconductor

2.8.5 Bus-Released State
In this state the bus is released to a bus master other than the CPU, in response to a bus request.
The bus masters other than the CPU are the DMA controller, the refresh controller, and an external
bus master. While the bus is released, the CPU halts except for internal operations. Interrupt
requests are not accepted. For details see section 6.3.7, Bus Arbiter Operation.
2.8.6 Reset State
When the RES input goes low all current processing stops and the CPU enters the reset state. The
I bit in the condition code register is set to 1 by a reset. All interrupts are masked in the reset state.
Reset exception handling starts when the RES signal changes from low to high.
The reset state can also be entered by a watchdog timer overflow. For details see section 12,
Watchdog Timer.
2.8.7 Power-Down State
In the power-down state the CPU stops operating to conserve power. There are three modes: sleep
mode, software standby mode, and hardware standby mode.
Sleep Mode: A transition to sleep mode is made if the SLEEP instruction is executed while the
SSBY bit is cleared to 0 in the system control register (SYSCR). CPU operations stop
immediately after execution of the SLEEP instruction, but the contents of CPU registers are
retained.
Software Standby Mode: A transition to software standby mode is made if the SLEEP
instruction is executed while the SSBY bit is set to 1 in SYSCR. The CPU and clock halt and all
on-chip supporting modules stop operating. The on-chip supporting modules are reset, but as long
as a specified voltage is supplied the contents of CPU registers and on-chip RAM are retained.
The I/O ports also remain in their existing states.
Hardware Standby Mode: A transition to hardware standby mode is made when the STBY input
goes low. As in software standby mode, the CPU and all clocks halt and the on-chip supporting
modules are reset, but as long as a specified voltage is supplied, on-chip RAM contents are
retained.
For further information see section 20, Power-Down State.
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