MC68HC908GZ8 Datasheet, PDF (116/344 Pages) Motorola, Inc – Microcontrollers

Central Processor Unit (CPU)
10.4 Arithmetic/Logic Unit (ALU)
The ALU performs the arithmetic and logic operations defined by the instruction
set.
Refer to the CPU08 Reference Manual (Freescale document order number
CPU08RM/AD) for a description of the instructions and addressing modes and
more detail about the architecture of the CPU.
10.5 Low-Power Modes
The WAIT and STOP instructions put the MCU in low power-consumption standby
modes.
10.5.1 Wait Mode
The WAIT instruction:
• Clears the interrupt mask (I bit) in the condition code register, enabling
interrupts. After exit from wait mode by interrupt, the I bit remains clear. After
exit by reset, the I bit is set.
• Disables the CPU clock
10.5.2 Stop Mode
The STOP instruction:
• Clears the interrupt mask (I bit) in the condition code register, enabling
external interrupts. After exit from stop mode by external interrupt, the I bit
remains clear. After exit by reset, the I bit is set.
• Disables the CPU clock
After exiting stop mode, the CPU clock begins running after the oscillator
stabilization delay.
10.6 CPU During Break Interrupts
If a break module is present on the MCU, the CPU starts a break interrupt by:
• Loading the instruction register with the SWI instruction
• Loading the program counter with $FFFC:$FFFD or with $FEFC:$FEFD in
monitor mode
The break interrupt begins after completion of the CPU instruction in progress. If
the break address register match occurs on the last cycle of a CPU instruction, the
break interrupt begins immediately.
A return-from-interrupt instruction (RTI) in the break routine ends the break
interrupt and returns the MCU to normal operation if the break interrupt has been
deasserted.
Data Sheet
116
Central Processor Unit (CPU)
MC68HC908GZ8
Freescale Semiconductor