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 R.K.Tiwari(ravikumar.tiwari@raisoni.net) 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 R.K.Tiwari(ravikumar.tiwari@raisoni.net)  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 R.K.Tiwari(ravikumar.tiwari@raisoni.net) Structure of Assembly language ORG 0H ;start (origin) at 0 MOV R5,#25H ;load 25H into R5 MOV R7,#34H ;load 34H into R7 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 R.K.Tiwari(ravikumar.tiwari@raisoni.net)  An Assembly language instruction consists of four fields: [label : ] mnemonic [operands] [;comment]

ASSEMBLING AND RUNNING AN 8051 PROGRAM R.K.Tiwari(ravikumar.tiwari@raisoni.net) 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 R.K.Tiwari(ravikumar.tiwari@raisoni.net)

ASSEMBLING AND RUNNING 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 R.K.Tiwari(ravikumar.tiwari@raisoni.net)

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 R.K.Tiwari(ravikumar.tiwari@raisoni.net)

THE PROGRAM COUNTER AND ROM SPACE IN THE 8051  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 R.K.Tiwari(ravikumar.tiwari@raisoni.net)

THE PROGRAM COUNTER AND ROM SPACE IN THE 8051  Placing code in program ROM  the opcode and operand are placed in ROM locations starting at memory 0000 R.K.Tiwari(ravikumar.tiwari@raisoni.net)

8051 DATA TYPES AND DIRECTIVES  8051 data type and directives ◦ DB (define byte) ◦ ORG (origin) ◦ EQU (equate) ◦ END directive R.K.Tiwari(ravikumar.tiwari@raisoni.net)

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 R.K.Tiwari(ravikumar.tiwari@raisoni.net)

8051 FLAG BITS AND THE PSW REGISTER  PSW (program status word) register R.K.Tiwari(ravikumar.tiwari@raisoni.net) 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 R.K.Tiwari(ravikumar.tiwari@raisoni.net) Figure 2–5 RAM Allocation in the 8051

8051 REGISTER BANKS AND STACK  Register banks in the 8051 R.K.Tiwari(ravikumar.tiwari@raisoni.net) Figure 2–6 8051 Register Banks and their RAM Addresses

8051 REGISTER BANKS AND STACK  How to switch register banks R.K.Tiwari(ravikumar.tiwari@raisoni.net) Table 2–2 PSW Bits Bank Selection

Viewing Register contents in Keil R.K.Tiwari(ravikumar.tiwari@raisoni.net) Figure 2–9 Register’s Screen from Keil Simulator

Memory window in Keil R.K.Tiwari(ravikumar.tiwari@raisoni.net) 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. R.K.Tiwari(ravikumar.tiwari@raisoni.net)

8051 Assembly Language Programming

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8051 Assembly Language Programming