The document provides an introduction to 8051 assembly language programming. It discusses that CPUs can only work with binary but programming in 0s and 1s is tedious for humans. Assembly language was developed to provide mnemonics for machine code instructions and make programming faster and less error prone. It also summarizes key aspects of 8051 architecture like registers, memory allocation, timers and counters.

1. 8051 ASSEMBLY
LANGUAGE
PROGRAMMING
BY
AVINASH KUMAR MISHRA

2. INTRODUCTION
TO PROGRAMMING:
CPU CAN ONLY WORK IN BINARY,IT CAN DO
SO AT VERY FAST SPEED.FOR HUMAN IT IS
QUITE TEDIOUS AND SLOW TO DEAL WITH
0’S & 1’S IN ORDER TO PROGRAM THE
COMPUTER .A PROGRAM THAT CONSISTS OF
0s AND 1s IS CALLED MACHINE LANGUAGE.
ASSEMBLY LANGUAGE WERE DEVELOPED
THAT
PROVIDED MNEUMONICS FOR THE MACHINE
CODE INSTRUCTION ,PLUS OTHER FEATURES

3. THAT MADE PROGRAMMING FASTER AND
.
LESS
PRONE TO ERROR. ASSEMBLY LANGUAGE
PROGRAMS MUST BE TRANSLATED INTO MACHINE
CODE BY A PROGRAM CALLED ASSEMBLER. TO
PROGRAM IN ASSEMBLY LANGUAGE , THE PROGRAMMER MUST KNOW ALL THE REGISTERS
OF THE CPU AND THE SIZE OF EACH ,AS WELL
AS OTHER DETAILS.

4. STRUCTURE
OF ASSEMBLY LANGUAGE
AN ASSEMBLY LANGUAGE CONSISTS OF
FOUR
FIELDS.
“ [LABEL:] MNEUMONICS [OPERAND]
[;COMMENT] ”
HERE BRACKETS INDICATE THAT A FIELD IS
OPTIONAL .

5. EXAMPLE
ORG OOH
;START AT LOCATION 0
MOV R5,#25H ;LOAD 25H INTO R5
MOV R6,#20H ; LOAD 20H INTO R6
MOV A ,#00H ; LOAD 00H INTO A
ADD A ,R5
; ADD CONTENTS OF R5 TO A
ADD A ,R6 ; ADD CONTENTS OF R6 TO A
ADD A ,#12H ; NOW A=A+ 12H
HERE: SJMP HERE ; STAY IN THIS LOOP
END

6. STEPS TO CREATE A
PROGRAM :
EDITOR PROGRAM
ASSEMBLER PROGRAM
LINKER PROGRAM
OH PROGRAM

7. PROGRAM COUNTER:
IT IS SPECIAL FUNCTION REGISTER
WHICH GENERALLY TELL OUR CONTROLLER OR PROCESSOR ABOUT NEXT
EXECUTING PROCESS.

8. STACK
POINTER:
IT IS THE SPECIAL FUNCTION REGISTER
WHICH IS USED TO STORE THE
EXECUTED
PROGRAM INSIDE YOUR STACK
MEMORY.
IT GENERALLY WORK ON THE
PHENOMENA
LIFO( LAST IN FIRST OUT).

9. ASSEMBLER
DIRECTIVES:
 ORG(ORIGIN):USED TO INDICATE THE
BEGINNING OF THE ADDERESS .
 EQU(EQUATE): USED TO DEFINE A
CONSTANT WITHOUT COPYING A
MEMORY LOCATION.
 END: IT INDICATES TO THE ASSEMBLER
THE
END OF SOURCE(ASM ) FILE.

10. PROGRAM
STATUS
WORD(PSW):

11. DEFINITION OF PSW REGISTER:
THE PROGRAM STATUS WORD (PSW) REGISTER IS AN 8 - BIT REGISTER. IT IS ALSO
REFFERED TO AS FLAG REGISTER.ALTHOUGH
PSW REGISTER IS 8-BITS WIDE, OLY 6-BITS
ARE USED BY 8051 . THE OTHER TWO ARE
USER DEFINABLE FLAGS. FOUR OF FLAGS
ARE CALLED CONDITIONAL FLAGS ,MEANS
THAT THEY INDICATE SOME CONDITION

12. CONTINUE
THAT RESULT AFTER A INSTRUCTION IS
EXECUTED . THESE FOUR ARE CY (CARRY)
,AC(AUXILIARY CARRY) , P ( PARITY) AND
OV(OVERFLOW) .RS0 AND RS1 ARE USED
TO CHANGE BANK REGISTORS . THE PSW
.1 AND PSW.5 ARE GENERAL PURPOSE
STATUS FLAG BITS AND CAN BE USED BY
PROGRAMMER FOR ANY PURPOSE.

13. 8051 REGISTER BANKS & STACK:
THERE ARE 32 BYTES OF RAM ARE SET
ASIDE FOR THE REGISTER BANKS AND
STACK. THERE ARE 128 BYTES OF RAM
ARE USED IN 8051 . THE 128 BYTES ARE
ASSIGNED ADDRESSES 00 TO 7FH. FROM
THESE 32 BYTES ARE USED FOR STACK
AND REGISTER BANK .

14. THERE ARE 4 REGISTER BANKS. THESE ARE
[1] BANK(0) : ADDRESS FROM 00H TO 07H.
[2] BANK(1) : ADDRESS FROM 08H TO 0FH.
[3] BANK(1) : ADDRESS FROM 10H TO 17 H.
[4] BANK(1) : ADDRESS FROM 18H TO 1FH.
FROM 20H TO 2FH ARE ASSIGNED FOR BITADDERESSABLE RAM AND FROM 30H TO 7F
H ARE FOR SCRATCH PAD RAM.

15. RAM ALLOCATION

16. 8051 REGISTER BANKS & THEIR
RAM ADDERESSES

17. STACK IN THE 8051:
STACK SI THE SECTION OF RAM USED BY
CPU TO STORE INFORMATION TEMPORA –
RILY . THIS INFORMATION COULD BE DATA
OR ADDERESS . THE CPU NEEDS THIS AREA
FOR STORAGE SINCE THERE ARE ONLY A
LIMITED NUMBER OF REGISTERS.

18. PUSHING ONTO STACK:
WE PUSH DATA ONTO STACK,THE STACK
POINTER (SP) IS INCREMENTED BY ONE.
• EXAMPLE:
MOV R6,#25H
MOV R1,#12H
MOV R4,#0F3H
PUSH 6
PUSH 1
PUSH 4

19. SOLUTION:
AFTER
PUSH6
0B
0A
09
08 25
AFTER
PUSH1
0B
0A
09 12
08 25
START
SP=07 SP=08
SP=09
0B
0A
09
08
AFTER
PUSH 4
0B
0A
F3
09
12
08 25
SP=0A

20. POPPING FROM STACK:

21. PROGRAMMING 8051 TIMERS:
• THE 8051 HAS TWO TIMERS : TIMER0
TIMER1.
• TIMER0 AND TIMER1 ARE 16-BITS WIDE.
• THE 8051 HAS 8-BIT ARCHITECTURE ,
EACH IS ACCESSED BY TWO SEPARATE
REGISTERS OF LOW BYTE AND HIGH
BYTE.

22. • TIMER0 REGISTERS: THE 16-BIT REGISTER
OF TIMER0 IS ACCESSED AS LOW BYTE
AND HIGH BYTE i.e TL0 & TH0.
• TIMER1 REGISTERS: THE 16-BIT REGISTER
OF TIMER0 IS ACCESSED AS LOW BYTE
AND HIGH BYTE i.e TL1 & TH1.
• TMOD (TIMER MODE) REGISTER: BOTH
TIMERS 0 &1 USE SAME REGISTER TMOD.

23. FIGURE OF TIMER0 AND TIMER1

24. TMOD REGISTER

25. STEPS TO PROGRAM FOR MODE1
a) LOAD TMOD
b) LOAD TH & TL
c) START TIMER (SBIT TR)
d) SET TI MER FLAG
H:JNB TF,H
e) CLR TR
f) CLR TF
g) RET

26. STEPS TO PROGRAM FOR MODE2
a) LOAD TMOD REGISTER
b) LOAD TIMER TYPE
c) SET TIMER/START TI MER
d) SET FLAG
e) CLR FLAG
f) RET

27. COUNTERS
TIMER / COUNTERS ARE USED TO
GENERATE TIME DELAYS . THESE
TIMERS CAN BE USED AS COUNTERS
COUNTING EVENTS HAPPENING OUTSIDE THE 8051 . WHEN THE TIMER /
COUNTER IS USED AS A TIMER, THE
8051’S CRYSTAL IS USED AS THE SOURCE
OF FREQUENCY.

28. .
END

29. .
THANK YOU