8051 Assembly Language Programming

8051 ASSEMBLY
LANGUAGE
PROGRAMMING
Ravikumar Tiwari
Assistant Professor
Dept. of Electronics Engineering, GHRCE, Nagpur

INSIDE THE 8051
R.K.Tiwari(ravikumar.tiwari@raisoni.net)
 most widely used registers are A, B, R0,
R1, R2, R3, R4, R5, R6, R7, DPTR and PC
 all registers are 8-bits, except DPTR and
the program counter which are 16 bit
 register A is used for all arithmetic and logic
instructions
 simple instructions MOV and ADD

INSIDE THE 8051
MOV instruction
MOV destination, source ;copy source to
destination
MOV A,#55H ;load value 55H into reg A
MOV R0,A ;copy contents of A into R0 (A=R0=55H)
MOV R1,A ;copy contents of A into R1
(A=R0=R1=55H)
MOV R2,A ;copy contents of A into R2
(A=R0=R1=R2=55H)
MOV R3,#95H ;load value 95H into R3 (R3=95H)
MOV A,R3 ;copy contents of R3 into A (A=R3=95H)

INSIDE THE 8051
 ADD instruction
◦ ADD A, source ;ADD the source operand
;to the accumulator
MOV A,#25H ;load 25H into A
MOV R2,#34H ;load 34H into R2
ADD A,R2 ;add R2 to accumulator
Executing the program above results in A = 59H

INTRODUCTION TO 8051
ASSEMBLY PROGRAMMING
Structure of Assembly language
ORG 0H ;start (origin) at 0
MOV A,#0 ;load 0 into A
ADD A,R5 ;add contents of R5 to A
;now A = A + R5
ADD A,R7 ;add contents of R7 to A
;now A = A + R7
ADD A, #12H;add to A value 12H
;now A = A + 12H
HERE: SJMP HERE ;stay in this loop
END ;end of asm source file
;Program 2-1: Sample of an Assembly Language Program

ASSEMBLING AND RUNNING
AN 8051 PROGRAM
 An Assembly language instruction
consists of four fields:
[label : ] mnemonic [operands]
[;comment]

AN 8051 PROGRAM
Figure 2–2 Steps to Create a Program

ASSEMBLING AND RUNNING AN
8051 PROGRAM
 More about "a51" and "obj" files
 "asm" file is source file and for this reason
some assemblers require that this file have
the “a51" extension
 this file is created with an editor such as
Windows Notepad or uVision editor
 uVision assembler converts the a51
assembly language instructions into
machine language and provides the obj file
 assembler also produces the Ist file

AN 8051 PROGRAM
 Ist file (list file)
 lst file is useful to the programmer because it lists all the
opcodes and addresses as well as errors that the
assembler detected
 uVision assumes that the list file is not wanted unless
you indicate that you want to produce it
 file can be accessed by an editor such as Note Pad and
displayed on the monitor or sent to the printer to
produce a hard copy
 programmer uses the list file to find syntax errors
 only after fixing all the errors indicated in the lst file that
the obj file is ready to be input to the linker program

THE PROGRAM COUNTER
AND ROM SPACE IN THE 8051
 Program counter in the 8051
 16 bits wide
 can access program addresses 0000
to FFFFH
 total of 64K bytes of code

THE PROGRAM COUNTER
 Where the 8051 wakes up when it is
powered up:
 wakes up at memory address 0000
when it is powered up
 first opcode must be stored at ROM
address 0000H

THE PROGRAM COUNTER
 Placing code in program ROM
 the opcode and operand are placed in
ROM locations starting at memory
0000

8051 DATA TYPES AND
DIRECTIVES
 8051 data type and directives
◦ DB (define byte)
◦ ORG (origin)
◦ EQU (equate)
◦ END directive

8051 DATA TYPES AND
DIRECTIVES
 Rules for labels in Assembly language
◦ each label name must be unique
◦ first character must be alphabetic
◦ reserved words must not be used as
labels

8051 FLAG BITS AND THE
PSW REGISTER
 PSW (program status word) register
Figure 2–4 Bits of the PSW Register

8051 FLAG BITS AND THE
PSW REGISTER
R.K.Tiwari(ravikumar.tiwari@raisoni.net)Table 2–1 Instructions That Affect Flag Bits

8051 REGISTER BANKS AND
STACK
 RAM memory space allocation in the
8051
Figure 2–5
RAM Allocation in the 8051

STACK
 Register banks in the 8051
Figure 2–6 8051 Register Banks and their RAM Addresses

STACK
 How to switch register banks
Table 2–2 PSW Bits Bank Selection

Viewing Register contents in
Keil
Figure 2–9 Register’s Screen from Keil Simulator

Memory window in Keil
Figure 2–10 128-Byte Memory Space from Keil Simulator

Problems
 Write an assembly program for
Addition, subtraction. Also write
register content in comment line after
executing that instruction.

8051 Assembly Language Programming

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