Freescale Semiconductor, Inc.
7
7
0
0
0
0
0
0
0
ACCUMULATOR A
ACCUMULATOR B
A
B
15
DOUBLE ACCUMULATOR D
INDEX REGISTER X
INDEX REGISTER Y
STACK POINTER
D
15
15
15
15
IX
IY
SP
PC
CCR
PROGRAM COUNTER
7
6
5
4
I
3
2
Z
1
0
CONDITION CODE REGISTER
S
X
H
N
V
C
CARRY
OVERFLOW
ZERO
NEGATIVE
I INTERRUPT MASK
HALF-CARRY (FROM BIT 3)
X INTERRUPT MASK
STOP DISABLE
Figure 3-1 Programming Model
3.1.1 Accumulators A, B, and D
Accumulators A and B are general-purpose 8-bit registers that hold operands and re-
sults of arithmetic calculations or data manipulations. For some instructions, these two
accumulators are treated as a single double-byte (16-bit) accumulator called accumu-
lator D. Although most instructions can use accumulators A or B interchangeably, the
following exceptions apply:
The ABX and ABY instructions add the contents of 8-bit accumulator B to the contents
of 16-bit register X or Y, but there are no equivalent instructions that use A instead of B.
The TAP and TPA instructions transfer data from accumulator A to the condition code
register, or from the condition code register to accumulator A, however, there are no
equivalent instructions that use B rather than A.
The decimal adjust accumulator A (DAA) instruction is used after binary-coded deci-
mal (BCD) arithmetic operations, but there is no equivalent BCD instruction to adjust
accumulator B.
CENTRAL PROCESSING UNIT
MC68HC11F1
3-2
TECHNICAL DATA
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