MC68HC11E Motorola, MC68HC11E Datasheet - Page 74

• Manufacturer Part Number: MC68HC11E
• Description: Microcontrollers
• Manufacturer: Motorola

Central Processor Unit (CPU)
4.2.1 Accumulators A, B, and D
Data Sheet
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Accumulators A and B are general-purpose 8-bit registers that hold operands and
results of arithmetic calculations or data manipulations. For some instructions,
these two accumulators are treated as a single double-byte (16-bit) accumulator
called accumulator D. Although most instructions can use accumulators A or B
interchangeably, these exceptions apply:
A
•
•
•
•
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 decimal (BCD) arithmetic operations, but there is no
equivalent BCD instruction to adjust accumulator B.
The add, subtract, and compare instructions associated with both A and B
(ABA, SBA, and CBA) only operate in one direction, making it important to
plan ahead to ensure that the correct operand is in the correct accumulator.
Freescale Semiconductor, Inc.
For More Information On This Product,
Figure 4-1. Programming Model
0
SP
PC
D
IX
IY
7
Go to: www.freescale.com
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Central Processor Unit (CPU)
S
X
H
I
B
N
Z
V
C
0
0
0
8-BIT ACCUMULATORS A & B
OR 16-BIT DOUBLE ACCUMULATOR D
INDEX REGISTER X
INDEX REGISTER Y
STACK POINTER
PROGRAM COUNTER
CONDITION CODES
CARRY/BORROW FROM MSB
OVERFLOW
ZERO
NEGATIVE
I-INTERRUPT MASK
HALF CARRY (FROM BIT 3)
X-INTERRUPT MASK
STOP DISABLE
M68HC11E Family — Rev. 5
MOTOROLA