Freescale Semiconductor, Inc.
GENERAL RELEASE SPECIFICATION
7
0
CONDITION CODE REGISTER
ACCUMULATOR
INDEX REGISTER
PCH
STACK
8
2
1
1
1
I
N
T
E
R
R
U
P
R
E
T
U
R
N
INCREASING
MEMORY
ADDRESSES
DECREASING
MEMORY
ADDRESSES
3
T
PCL
UNSTACK
4
NOTE: Since the stack pointer decrements during pushes, the PCL is stacked first,
followed by PCH, etc. Pulling from the stack is in the reverse order.
5
Figure 3-2. Stacking Order
6
3.2.1 Accumulator (A)
7
The accumulator is a general-purpose 8-bit register used to hold operands and
results of arithmetic calculations or data manipulations.
8
7
0
A
9
10
11
12
13
14
A
3.2.2 Index Register (X)
The index register is an 8-bit register used for the indexed addressing value to
create an effective address. The index register may also be used as a temporary
storage area.
7
0
X
16
17
18
19
20
CENTRAL PROCESSING UNIT
MC68HC805P18
3-2
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