Freescale Semiconductor, Inc.
Ce ntra l Proc e ssor Unit (CPU)
3.6 Prog ra m Counte r (PC)
The program counter is a 16-bit register that contains the address of the
next instruction or operand to be fetched as shown in Figure 3-5. The
three most significant bits of the program counter are ignored internally
and appear as 111 during stacking and subroutine calls.
Normally, the address in the program counter automatically increments
to the next sequential memory location every time an instruction or
operand is fetched. Jump, branch, and interrupt operations load the
program counter with an address other than that of the next sequential
location.
Bit
Bit
0
15 14 13 12 11 10
9
8
7
6
5
4
3
2
1
Read:
Write:
Reset:
1
0
1
0
1
0
Loaded with Vector from $1FFE and $1FFF
Figure 3-5. Program Counter (PC)
3.7 Cond ition Cod e Re g iste r (CCR)
The condition code register is an 8-bit register whose three most
significant bits are permanently fixed at 111 as shown in Figure 3-6. The
condition code register contains the interrupt mask and four flags that
indicate the results of the instruction just executed. The following
paragraphs describe the functions of the condition code register.
Bit 7
1
6
1
1
5
1
1
4
3
I
2
1
Bit 0
Z
Read:
Write:
Reset:
H
U
N
U
C
U
1
1
U
U = Unaffected
Figure 3-6. Condition Code Register (CCR)
General Release Specification
MC68HC705JJ7/MC68HC705JP7 — Rev. 3.0
Central Processor Unit (CPU)
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