e have included this appendix to save you the task of having to turn to secondary
material when writing 68000 assembly language programs. Since most
programmers are not interested in the encoding of instructions, details of
instruction encoding have been omitted (i.e., the actual op-code bit patterns).
Applications of some of the instructions have been provided to demonstrate how
they can be used in practice.
Instructions are listed by mnemonic in alphabetical order. The information
provided about each instruction is: its assembler syntax, its attributes (i.e., whether
it takes a byte, word, or longword operand), its description in words, the effect its
execution has on the condition codes, and the addressing modes it may take. The
effect of an instruction on the CCR is specified by the following codes:
The state of the bit is undefined (i.e., its value cannot be predicted)
The bit remains unchanged by the execution of the instruction
The bit is set or cleared according to the outcome of the instruction.
Unless an addressing mode is implicit (e.g.,
, etc.), the legal
source and destination addressing modes are specified by their assembly language
syntax. The following notation is used to describe the 68000’s instruction set.
Data and address register direct.
Address register indirect.
Address register indirect with post-incrementing or pre-
Address register indirect with displacement, and address
register indirect with indexing and a displacement.
Absolute addressing with a 16-bit or a 32-bit address.
Program counter relative addressing with a 16-bit offset,
or with an 8-bit offset plus the contents of an index
An immediate value (i.e., literal) which may be 16 or 32
bits, depending on the instruction.
The 68000’s Instruction Set