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DSM85 User t s Manual
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3.10 Forvard Rererences
A for"ard reference is a reference to a symbol vhich is
not defined until later in the source program. For example,
take the folloving program fragment:
DS
GRINeH
EQU
DS
GRINCH+I
7
GRINCH+I
The use of GRINeR in the first DS statement 15 a for"ard
reference, since GRINeH has not yet been defined vhen this
statement is encountered. The use of GRINeR in the second
DS is not a forvard reference, as the statement defining
GRINeR bas already been encountered.
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There are a number of places in the assembly language
"here forvard references, and expressions containing them,
are specifically prohibited. The general rule is that a
forvard reference is not alloyed vhere the value of the
expression affects the location counter or controls the
number of bytes of code generated. Most cases vhere this
occurs are in pseudo-instructions; if' forvard ref'erences are
not allo"ed, this viII be stated In the p;eudo-op descrip­
tion. The assembler viII report an ifF" error vhenever it
finds an illegal forvard reference.
To further clarify the notion of a forvard reference,
consider the folloving statement:
JMP
$+5
Tbe expression $+5 is not a forvard reference, even though
the jump is forvard, because the value of the location
counter ($) is already knovn "hen the JMP statement is
processed.
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