4.9.53 Set Directive

The SET directive is equivalent to EQU (Equ Directive), except that it allows a symbol to be re-defined in the same module without error. For example:

thomas SET 0h
; code using first value
thomas SET 44h
;code using second value

will equate the symbol thomas to the value 0, then later in the program, equate the same symbol to the different value 0x44.

This directive performs a similar function to that of the preprocessor’s #define directive (see Preprocessor Directives), which is often preferred in assembly programs to represent values with symbols.

Note that this directive does not create variables. It does not reserve any memory for the symbol created. Use the DS directive to reserve data memory associated with a label (see Ds Directive).

When working with multiple assembly modules, it's possible to have multiple local symbols with the same name. However, only SET symbols marked as globally accessible (see Global Directive) will be visible during debugging. The IDE will display the value of globally defined symbols, but the value of local symbols will be used by the code within the modules where they are defined. To avoid confusion, it's advisable not to define symbols with the same name in different modules.

For instance, in the following code:

GLOBAL mode
mode SET 2

the mode symbol will be watchable in IDEs, with an indicated "address" of 2.

Since SET directives do not contribute to the output, they are processed separately to other instructions and directives. Thus, the program location counter cannot be used in SET operand expressions.