MC68HC812A4 Datasheet, PDF (59/342 Pages) Motorola, Inc – 16-bit device composed of standard on-chip peripheral modules connected by an intermodule bus. Modules include

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Section 3. Central Processor Unit (CPU12)
3.1 Contents
3.2 Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .59
3.3 Programming Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .60
3.4 CPU Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .60
3.4.1 Accumulators A and B . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61
3.4.2 Accumulator D . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61
3.4.3 Index Registers X and Y. . . . . . . . . . . . . . . . . . . . . . . . . . . .62
3.4.4 Stack Pointer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .62
3.4.5 Program Counter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .63
3.4.6 Condition Code Register . . . . . . . . . . . . . . . . . . . . . . . . . . .63
3.5 Data Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .64
3.6 Addressing Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .65
3.7 Indexed Addressing Modes . . . . . . . . . . . . . . . . . . . . . . . . . . .66
3.8 Opcodes and Operands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .67
3.2 Overview
The CPU12 is a high-speed, 16-bit processor unit. It has full 16-bit data
paths and wider internal registers (up to 20 bits) for high-speed extended
math instructions. The instruction set is a proper superset of the
M68HC11instruction set. The CPU12 allows instructions with odd byte
counts, including many single-byte instructions. This provides efficient
use of ROM space. An instruction queue buffers program information so
the CPU always has immediate access to at least three bytes of machine
code at the start of every instruction. The CPU12 also offers an
extensive set of indexed addressing capabilities.
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MOTOROLA
Central Processor Unit (CPU12)
MC68HC812A4 — Rev. 3.0
59