MC68HC12 Datasheet, PDF (36/478 Pages) Motorola, Inc – The MC68HC912DT128A microcontroller unit (MCU) is a 16-bit device composed of standard on-chip peripherals including a 16-bit central processing unit

Central Processing Unit
2.3 Programming Model
CPU12 registers are an integral part of the CPU and are not addressed
as if they were memory locations.
7
A
15
15
15
15
15
07
B
D
0 8-BIT ACCUMULATORS A & B
OR
0 16-BIT DOUBLE ACCUMULATOR D
IX
0 INDEX REGISTER X
IY
0 INDEX REGISTER Y
SP
0 STACK POINTER
PC
0 PROGRAM COUNTER
S X H I N Z V C CONDITION CODE REGISTER
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.
Technical Data
36
Central Processing Unit
MC68HC912DT128A — Rev 4.0
MOTOROLA