Central Processor Unit (CPU)
CPU Registers
MC68HC11E Family
—
Rev. 4
Technical Data
MOTOROLA
Central Processor Unit (CPU)
47
Figure 3-1. Programming Model
3.3.1 Accumulators A, B, and D
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:
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.
8-BIT ACCUMULATORS A & B
OR 16-BIT DOUBLE ACCUMULATOR D
7
15
0
7
0
0
A
B
D
IX
IY
SP
PC
7
0
C
V
Z
N
I
H
X
S
INDEX REGISTER X
INDEX REGISTER Y
STACK POINTER
PROGRAM COUNTER
CARRY/BORROW FROMMSB
OVERFLOW
ZERO
NEGATIVE
I-INTERRUPT MASK
HALF CARRY (FROM BIT 3)
X-INTERRUPT MASK
STOP DISABLE
CONDITION CODES