MC68HC11F1_13 Datasheet, PDF (26/158 Pages) Freescale Semiconductor, Inc – Technical Data

Freescale Semiconductor, Inc.
7
0
ACCUMULATOR A
A
7
0
ACCUMULATOR B
B
15
0
DOUBLE ACCUMULATOR D
D
15
0
INDEX REGISTER X
IX
15
0
INDEX REGISTER Y
IY
15
0
STACK POINTER
SP
15
0
PROGRAM COUNTER
PC
7 65432 10
CONDITION CODE REGISTER S X H I N Z V C CCR
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
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