4.9.17 Equ Directive

The EQUdirective defines a symbol and equates this to the value of its constant expression argument. For example:

thomas EQU 123h
engine EQU thomas

will equate the identifiers thomas and engine with the value 123h.

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.

The EQU directive is legal only when the symbol has not previously been defined in the same module. See the SET directive (Set Directive) if symbol values need to be redefined at different points in the same source file.

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 EQU 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 example, in the following code:

GLOBAL mode
mode EQU 2

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

Since EQU 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 EQU operand expressions.