Keil Software — A51/AX51/A251 Macro Assembler and Utilities

99

The directives should not be confused with instructions. They do not produce

executable code, and with the exception of the DB, DW and DD directives, they

have no direct effect on the contents of code memory. These directives change

the state of the assembler, define user symbols, and add information to the object

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file.

The following table provides an overview of the assembler directives. Page

refers to the page number in this user’s guide where you can find detailed

information about the directive.

Directive / Page

Format

Description

BIT

114

symbol BIT bit_address

Define a bit address in bit data space.

BSEG

111

BSEG

[AT absolute address]

Define an absolute segment within the

bit address space.

CODE

114

symbol CODE code_address

Assign a symbol name to a specific

address in the code space.

CSEG

111

CSEG

[AT absolute address]

Define an absolute segment within the

code address space.

DATA

114

symbol

DATA data_address

Assign a symbol name to a specific

on-chip data address.

DB

119

[label:]

DB expression [, expr ...]

Generate a list of byte values.

DBIT

122

[label:] DBIT expression

Reserve a space in bit units.

DD

121

[label:]

DD expression [, expr ...]

Generate a list of double word values.

DS

123

[label:] DS expression

Reserve space in byte units.

DSB

124

[label:] DSB expression

Reserve space in byte units.

DSD

126

[label:] DSD expression

Reserve space in double word units.

DSEG

111

DSEG

[AT absolute address]

Define an absolute segment within the

indirect internal data space.

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Chapter 4. Assembler Directives

Directive / Page

Format

Description

DSW

125

[label:]

DSW expression

Reserve space in word units;

advances the location counter of the

current segment.

DW

120

[label:]

DW expression [, expr. ...]

Generate a list of word values.

END

136

END

Indicate end of program.

EQU

113

EQU expression

Set symbol value permanently.

_ _ERROR_ _136

_ _ERROR_ _ text

Generate a standard error message.

EVEN

134

EVEN

Ensure word alignment for variables.

EXTRN

131

EXTRN class

(symbol [, ...])

Defines symbols referenced in the

[:type]

EXTERN

EXTERN class [:type] (symbol [, ...])

current module that are defined in

other modules.

IDATA

114

symbol

IDATA idata_address

Assign a symbol name to a specific

indirect internal address.

ISEG

111

ISEG [AT absolute address]

Define an absolute segment within the

internal data space.

LABEL

129

name[:]

LABEL [type]

Assign a symbol name to a address

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location within a segment.

LIT

116

symbol

LIT ’literal string’

Assign a symbol name to a string.

NAME

132

NAME modulname

Specify the name of the current

module.

ORG

133

ORG expression

Set the location counter of the current

segment.

PROC

127

name PROC [type]

Define a function start and end.

ENDP

name ENDP

PUBLIC

130

PUBLIC symbol [, symbol ...]

Identify symbols which can be used

outside the current module.

RSEG

110

RSEG

seg

Select a relocatable segment.

SEGMENT

106

seg SEGMENT class [reloctype]

Define a relocatable segment.

[alloctype]

SET

113

SET expression

Set symbol value temporarily.

sfr,

116

sfr symbol = address;

Define a special function register

sfr16

sfr16 symbol = address;

(SFR) symbol or a SFR bit symbol.

sbit

sbit symbol = address;

USING

134

USING

expression

Set the predefined symbolic register

address and reserve space for the

specified register bank.

XDATA

114

symbol

XDATA xdata_address

Assign a symbol name to a specific

off-chip data address.

XSEG

111

XSEG

[AT absolute address]

Define an absolute segment within the

external data address space.

Keil Software — A51/AX51/A251 Macro Assembler and Utilities

101

Segment Control

Generic Segments: SEGMENT, RSEG

Absolute Segments: CSEG, DSEG, BSEG, ISEG, XSEG

Symbol Definition

Generic Symbols: EQU, SET

Address Symbols: BIT, CODE, DATA, IDATA, XDATA

SFR Symbols:

sfr, sfr16, sbit

Text Replacement: LIT

Memory Initialization

DB, DW,

DD

Memory Reservation

DBIT, DS,

DSB, DSW, DSD

Procedure Declaration

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PROC / ENDP, LABEL

Program Linkage

PUBLIC, EXTRN /

EXTERN

, NAME

Address Control

ORG,

EVEN

, USING

Others

END, _ _ERROR_ _