mc68hc916y3 Freescale Semiconductor, Inc, mc68hc916y3 Datasheet - Page 95

• Manufacturer Part Number: mc68hc916y3
• Description: Mc68hc16y3 16 Bit Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

4.9 Instruction Format
MC68HC16Y3/916Y3
USER’S MANUAL
CPU16 instructions consist of an 8-bit opcode that can be preceded by an 8-bit prebyte
and followed by one or more operands.
Opcodes are mapped in four 256-instruction pages. Page 0 opcodes stand alone.
Page 1, 2, and 3 opcodes are pointed to by a prebyte code on page 0. The prebytes
are $17 (page 1), $27 (page 2), and $37 (page 3).
Operands can be four bits, eight bits or sixteen bits in length. Since the CPU16 fetches
16-bit instruction words from even-byte boundaries, each instruction must contain an
even number of bytes.
Operands are organized as bytes, words, or a combination of bytes and words.
Operands of four bits are either zero-extended to eight bits, or packed two to a byte.
The largest instructions are six bytes in length. Size, order, and function of operands
are evaluated when an instruction is decoded.
A page 0 opcode and an 8-bit operand can be fetched simultaneously. Instructions that
use 8-bit indexed, immediate, and relative addressing modes have this form. Code
written with these instructions is very compact.
Figure 4-4 shows basic CPU16 instruction formats.
Freescale Semiconductor, Inc.
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MOTOROLA
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