Central Processor Unit (CPU)
CPU Registers
MC68HC908MR16/MC68HC908MR32 — Rev. 4.0 Advance Information
MOTOROLA Central Processor Unit (CPU) 75
6.4.4 Program Counter
The program counter (PC) is a 16-bit register that cont ains the address
of the next instruction or operand to be fetched.
Normally, the program counter automatically increments to the next
sequential memory location every time an instr uc tion or operand is
fetched. Jump, branch, and interrupt operations load the program
counter with an address other than that of the next sequential location.
During reset, the program counter is loaded with the reset vector
address located at $FFFE and $FFFF. The vector address is the
address of the first instruction to be executed afte r exiting the re set state.
6.4.5 Condition Code Register
The 8-bit condition code register (CCR) contains the interrupt m ask and
five flags that indicate the results of the instruction just executed. Bits 6
and 5 are set permanently to logic 1. The functio ns of the condit ion code
register are described here.
Bit
151413121110987654321
Bit
0
Read:
Write:
Reset: Loaded with vector from $FFFE and $FFFF
Figure 6-5. Program Counter (PC)
Bit 7654321Bit 0
Read: V11HI NZC
Write:
Reset:X11X1XXX
X = Indeterminate
Figure 6-6. Condition Code Register (CCR)