VI XỬ LÝ 8051 chap7 assembly programming

FIGURE 7–3 Use of the generic JMP mnemonic Symbol Table : Symbol →Address/Data • Assembly program – Machine instructions – Assembler Directives • Like Variable declaration in high-level

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)

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

FIGURE 7–3 Use of the generic JMP mnemonic

Symbol Table :

Symbol →Address/Data

• Assembly program

– Machine instructions

– Assembler Directives

• Like Variable declaration in high-level language

– Assembler controls

• Conditional compiling

– Comments

After ; to EOL

• Formant of Assembly language

– case insensitive

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

Example :

…

• Constant expression

– Implement by assembler

Examples:

• Operators in constant expressions

– Arithmetic : + - * / MOD

– Logic : AND OR NOT XOR

– Relational : EQ NE LT LE GT GE

= <> < <= > >=

– Special : SHR SHL HIGH LOW ()

• 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

(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

… ; 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

(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

…

MOV R7, #LENGTH MOV R0, #BUFFER

BJNZ R7, LOOP

….

END

Example 2:

XSEG AT 4000H

…

MOVX @DPTR, A

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

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

….

END

FIGURE 7–4 Use of the EXTRN and PUBLIC assembler directives

Multi-file : EXTERN, PUBLIC directive

(3) Program link

FIGURE 7–5 Defining and initiating absolute and relocatable segments

RSEG directive – reallocatable segment

FIGURE 7–6 Assembler controls supported by ASM51

FIGURE 7–7 Linker operation

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

(c) EXAMPLE.M51

Output of linkage editor -Symbol table

-Reallocatable address were computed already