M68HC11 Datasheet, PDF (47/336 Pages) Motorola, Inc – Technical Data

Central Processor Unit (CPU)
CPU Registers
7
A
07
B
15
D
0 8-BIT ACCUMULATORS A & B
0 OR 16-BIT DOUBLE ACCUMULATOR D
IX
INDEX REGISTER X
IY
INDEX REGISTER Y
SP
STACK POINTER
PC
7
0
SXH I NZVC
PROGRAM COUNTER
CONDITION CODES
CARRY/BORROW FROM MSB
OVERFLOW
ZERO
NEGATIVE
I-INTERRUPT MASK
HALF CARRY (FROM BIT 3)
X-INTERRUPT MASK
STOP DISABLE
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.
MC68HC11E Family — Rev. 4
MOTOROLA
Central Processor Unit (CPU)
Technical Data
47