STC89C53RC datasheet(147/165 Pages) STC

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Public

The format for the PUBLIC (public symbol) directive is

PUBLIC

symbol

[, symbol] […]

The PUBLIC directive allows the list of specified symbols to known and used outside the currently assembled

module. A symbol declared PUBLIC must be defined in the current module. Declaring it PUBLIC allows it to be

referenced in another module. For example,

PUBLIC

INCHAR, OUTCHR, INLINE, OUTSTR

Extrn

The format for the EXTRN (external symbol) directive is

EXTRN

segment_type (symbol [, symbol] […], …)

The EXTRN directive lists symbols to be referenced in the current module that are defined in other modules. The

list of external symbols must have a segment type associated with each symbol in the list. (The segment types

are CODE, XDATA, DATA, IDATA, BIT, and NUMBER. NUMBER is a type-less symbol defined by EQU.)

The segment type indicates the way a symbol may be used. The information is important at link-time to ensure

symbols are used properly in different modules.

The PUBLIC and EXTRN directives work together. Consider the two files, MAIN.SRC and MESSAGES.

SRC. The subroutines HELLO and GOOD_BYE are defined in the module MESSAGES but are made available

to other modules using the PUBLIC directive. The subroutines are called in the module MAIN even though they

are not defined there. The EXTRN directive declares that these symbols are defined in another module.

MAIN.SRC:

EXTRN

CODE (HELLO, GOOD_BYE)

…

CALL

HELLO

…

CALL

GOOD_BYE

…

END

MESSAGES.SRC:

PUBLIC

HELLO, GOOD_BYE

…

HELLO:

(begin subroutine)

…

RET

GOOD_BYE:

(begin subroutine)

…

RET

…

END

Neither MAIN.SRC nor MESSAGES.SRC is a complete program; they must be assembled separately and

linked together to form an executable program. During linking, the external references are resolved with correct

addresses inserted as the destination for the CALL instructions.

Name

The format for the NAME directive is

NAME module_name

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