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Assembly Language Fundamentals
51
Assembly Language Source
You may have recognized the assembly language instruction and pseudo-instructions to the
right of ISOURCE in the examples above. This is where your instructions and pseudo-
instructions appear. However, the source is a little more versatile than that. In general, {assem-
bly language source} has the syntax -
[ {label}
] {action} [
{comment} ]
Or, the action may be omitted and only a comment appears -
[{label} ::]
!
{comment}
A label is always optional in the source, but either an {action} or a {comment} must be present
in every source line.
Actions
An {action} in assembly language source is -
• A machine instruction, with any operand it may require. These were discussed at some
length in Chapter 3 .
• A pseudo-instruction, with any operand it may require. These are discussed under the
topics to which they relate.
The actions contained in the above example were -
Labels
The {label} in assembly language source is part of the symbolic addressing capability of the
assembler. This {label} is used by the assembler only. Neither the operating system nor BASIC
is aware of its existence.
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