STC89LE53RC datasheet(143/165 Pages) STC

143 / 165 page

MOV

PSW, #00011000B

;SELECT REGISTER BANK 3

USING 3

PUSH

AR7

;ASSEMBLE TO PUSH 1FH

MOV

PSW, #00001000B

;SELECT REGISTER BANK 1

USING 1

PUSH

AR7

;ASSEMBLE TO PUSH 0FH

Symbol Definition

The symbol definition directives create symbols that represent segment, registers, numbers, and addresses. None

of these directives may be preceded by a label. Symbols defined by these directives may not have been previously

defined and may not be redefined by any means. The SET directive is the only exception. Symbol definiton

directives are described below.

Segment

The format for the SEGMENT directive is shown below.

symbol

SEGMENT

segment_type

The symbol is the name of a relocatable segment. In the use of segments, ASM51 is more complex than

conventional assemblers, which generally support only "code" and "data" segment types. However, ASM51

defines additional segment types to accommodate the diverse memory spaces in the 8051. The following are the

defined 8051 segment types (memory spaces):

CODE (the code segment)

XDATA (the external data space)

DATA (the internal data space accessible by direct addressing, 00H–07H)

IDATA (the entire internal data space accessible by indirect addressing, 00H–07H)

BIT (the bit space; overlapping byte locations 20H–2FH of the internal data space)

•

For example, the statement

EPROM

SEGMENT

CODE

declares the symbol EPROM to be a SEGMENT of type CODE. Note that this statement simply declares what

EPROM is. To actually begin using this segment, the RSEG directive is used (see below).

EQU (Equate)

The format for the EQU directive is

Symbol

EQU

expression

The EQU directive assigns a numeric value to a specified symbol name. The symbol must be a valid symbol

name, and the expression must conform to the rules described earlier.

The following are examples of the EQU directive:

N27

EQU

;SET N27 TO THE VALUE 27

HERE

EQU

;SET "HERE" TO THE VALUE OF

;THE LOCATION COUNTER

EQU

0DH

;SET CR (CARRIAGE RETURN) TO 0DH

MESSAGE:

DB 'This is a message'

LENGTH

EQU

$ - MESSAGE

;"LENGTH" EQUALS LENGTH OF "MESSAGE"

Other Symbol Definition Directives

The SET directive is similar to the EQU directive except the

symbol may be redefined later, using another SET directive.

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