8051 Chap7 Assembly Programming

7/30/2019 8051 Chap7 Assembly Programming

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Chapter 7

Assembly Language Programming

Chap 7 Assembly LanguageProgramming

Assembler

Change mnemonic code into machine code

Label can be used to represent symbolic address/data

Directives : like pre-processing operator (#) in Clanguage.

Linkage Editor

Link objective code into executable file

(*.obj *.exe)


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FIGURE 71 Assembling a source program

Assembler

FIGURE 72 Pseudo code sketch of a two-pass operator

PASS 1

Establish symbol table

- Computing

address/symbol

PASS 2

Convert mnemonic codeinto machine code


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FIGURE 73 Use of the generic JMP mnemonic

Symbol Table :

SymbolAddress/Data

Assembly program

Machine instructions

MOV A, #0

Assembler Directives

Like Variable declaration in high-level language

Assembler controls

Conditional compiling

Comments

After ; to EOL

. ; this is a comment


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Formant of Assembly language

case insensitive

[label:] mnemonic [operation] [,operand].. ; comment

Example :

PAR EQU 500 ; #define symbol

JNB TI, $ ; HERE: JNB TI, HERE

Constant expression Implement by assembler

Examples:

MOV A, 9-0 ; means char constant

Operators in constant expressions

Arithmetic : + - * / MOD

Logic : AND OR NOT XOR

Relational : EQ NE LT LE GT GE= < >=

Special : SHR SHL HIGH LOW ()


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Precedence of constant()

HIGH LOW

/MOD SHR SHL

+ -

EQ NE LT LE GT GE = < >=

NOT

AND

OR

XOR

Directives(1) Assembler state control

ORG define the location of the code

END directive to tell assembler the end of source file

USING set the register bank

Examples :

ORG 100H

ORG $+100H

USING 3

PUSH AR7 ; now AR7 means $23H.

END


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(2) Symbol define

Segment EQU

Storage initialization/reservation

Program link

Segment selection

(A) Segment defineIn low-level language, the programmer need to manage the

location of program/data in memory

symbol SEGMENT segment_type

.. ; the following program was form a segment

; called symbol,; The content is segment_type (code or data)

segment_type can be one of

CODE (program)

XDATA (the extended data segment)

DATA (direct address space, 00-7fH)

IDATA (indirect address space, 00-7FH 80-FFH for 8052)

BIT (bit address space)

CSEG AT (equivalent to SEGMENT CODE)

DSEG AT

XSEG AT

ISEG AT

BSEG AT


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(B) EQU

like the named constant define in C (#define)

Example:

BASE EQU 10

other constants :

#10H, $(current location)

(C) Storage initialization/reservation

DS (define space, like unintialized array)

DBIT (define bit data)

DB (define byte data) DW (define word data, low-byte in lower address)

Example 1:

DSEG AT 30H

LENGTH: EQU 40

BUFFER: DS LENGTH

PROG SEGMENT CODE

MOV R7, #LENGTH

MOV R0, #BUFFER

LOOP: MOV @R0, #0

BJNZ R7, LOOP

.

END


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Example 2:

XSEG AT 4000HXLENGTH: EQU 1000

XBUFFER: DS XLENGTH

PROG SEGMENT CODE

MOV DPTR, #XLENGTH

LOOP: CLR A

MOVX @DPTR, A

INC DTPR

MOV A, DPL

CJNE A, #LOW(XBUFFER+XLENGTH+1),LOOP

MOV A, DPH

CJNE A, #HIGH(XBUFFER+XLENGTH+1),LOOP

.END

FIGURE 74 Use of the EXTRN and PUBLIC assembler directives

Multi-file : EXTERN, PUBLIC directive(3) Program link


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FIGURE 75 Defining and initiat ing absolute and relocatable segments

RSEG directive reallocatable segment

FIGURE 76 Assembler controls supported by ASM51


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FIGURE 76 (continued) Assembler controls supported by ASM51

FIGURE 77 Linker operation


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FIGURE 78a Annotated example: linking relocatable segments and modules. (a) ECHO.LST. (b) IO.LST. (c)EXAMPLE.M51.

Address-relative content

Need to fix in linkage

- reallocatable

FIGURE 78a Annotated example: linking relocatable segments and modules. (a) ECHO.LST. (b) IO.LST. (c)

EXAMPLE.M51.

Symbol Table


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FIGURE 78d (continued) Annotated example: linking relocatable segments and modules. (a) ECHO.LST. (b) IO.LST.(c) EXAMPLE.M51.

Output of linkage editor

-Symbol table

-Reallocatable address were

computed already

8051 Chap7 Assembly Programming

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