VI XỬ LÝ 8051 chap7 assembly programming

17-May-12

Chapter 7
Assembly Language Programming

Chap 7 Assembly Language
Programming
• Assembler
– Change mnemonic code into machine code
– Label can be used to represent symbolic address/data
– Directives : like pre-processing operator (#) in C
language.

• Linkage Editor
– Link objective code into executable file
(*.obj → *.exe)

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FIGURE 7–1

Assembling a source program

Assembler

FIGURE 7–2

Pseudo code sketch of a two-pass operator

PASS 1 –
Establish symbol table
- Computing
address/symbol

PASS 2 –
Convert mnemonic code
into machine code

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FIGURE 7–3

Use of the generic JMP mnemonic

Symbol Table :
Symbol →Address/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 define
In 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
DBIT
DB
DW

(define space, like unintialized array)
(define bit data)
(define byte data)
(define word data, low-byte in lower address)

Example 1:

LENGTH:
BUFFER:
PROG
…

LOOP:

DSEG AT 30H
EQU
40
DS
LENGTH
SEGMENT
MOV
MOV
MOV
BJNZ

CODE

R7, #LENGTH
R0, #BUFFER
@R0, #0
R7, LOOP

….
END

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Example 2:

XLENGTH:
XBUFFER:
PROG
…

XSEG AT 4000H
EQU
1000
DS
XLENGTH
SEGMENT
MOV
CLR
MOVX
INC
MOV
CJNE
MOV
CJNE

LOOP:

CODE

DPTR, #XLENGTH
A
@DPTR, A
DTPR
A, DPL
A, #LOW(XBUFFER+XLENGTH+1),LOOP
A, DPH
A, #HIGH(XBUFFER+XLENGTH+1),LOOP

….
END

FIGURE 7–4

Use of the EXTRN and PUBLIC assembler directives

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

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FIGURE 7–5

Defining and initiating absolute and relocatable segments

RSEG directive – reallocatable segment

FIGURE 7–6

Assembler controls supported by ASM51

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FIGURE 7–6 (continued)

FIGURE 7–7

Assembler controls supported by ASM51

Linker operation

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FIGURE 7–8a
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 7–8a
Annotated example: linking relocatable segments and modules. (a) ECHO.LST. (b) IO.LST. (c)
EXAMPLE.M51.

Symbol Table

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FIGURE 7–8d (continued)
(c) EXAMPLE.M51.

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

Output of linkage editor
-Symbol table
-Reallocatable address were
computed already

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