Datasheet

Central Processing Unit
Technical Data MC68HC912DT128A — Rev 4.0
36 Central Processing Unit MOTOROLA
2.3 Programming Model
CPU12 registers are an integral part of the CPU and are not addressed
as if they were memory locations.
Figure 2-1. Programming Model
Accumulators A and B are general-purpose 8-bit accumulators used to
hold operands and results of arithmetic calculations or data
manipulations. Some instructions treat the combination of these two 8-
bit accumulators as a 16-bit double accumulator (accumulator D).
Index registers X and Y are used for indexed addressing mode. In the
indexed addressing mode, the contents of a 16-bit index register are
added to 5-bit, 9-bit, or 16-bit constants or the content of an accumulator
to form the effective address of the operand to be used in the instruction.
7
15
15
15
15
15
D
IX
IY
SP
PC
AB
NSXH I ZVC
0
0
0
0
0
0
70
CONDITION CODE REGISTER
8-BIT ACCUMULATORS A & B
16-BIT DOUBLE ACCUMULATOR D
INDEX REGISTER X
INDEX REGISTER Y
STACK POINTER
PROGRAM COUNTER
OR
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