Intro to 8051 Assembly Programming

8/3/2019 Intro to 8051 Assembly Programming

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Pari vallal Kannan

Center for Integrated Circuits and Systems

University of Texas at Dallas

8051 Microcontroller Architecture, Intro to AssemblyProgramming

EE4380 Fall 2002

Class 2


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Class 2: Objective

l 8051 internal architecture

l Register Set

l Instruction Set

l Memory Map

l Intro to Stack, SFRs

l Assembly language programming


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8051 Architecture

l Programmers View

Register Set

Instruction Set

Memory map

l Hardware Designers View

Pinout

Timing characteristics Current / Voltage requirements


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Programmers View Register Set

l Registers

A, B, R0 to R7 : 8 bit registers

DPTR : [DPH:DPL] 16 bit register

PC : Program Counter (Instruction Ptr) 16bits

4 sets of register bank R0-R7

Stack pointer SP

PSW : Program Status Word (a.k.a Flags)

SFR : Special Function Registers

l Control the on-board peripherals


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Assembly Absolute Basics

l Intel Assembly format

Operation destination source ; comment

l Values are to be preceded by a # sign

#55, #32 etc

l Hex values are to be followed by H

#55H, #32H

l If the first figure in a hex quantity is a letter (A-F) then a 0 mustprecede it

#0FFH, #0C1H, #0D2H


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Register Set Accumulator A, ACC

l Commonly used for moving data around, logicand arithmetic operations on 8bit data

l Examples

mov A, R0 ;copy contents of R0 to Apush ACC ;store A onto stack

mov A, #10 ;A 10

mov B, A ;B A

mov A, 10 ;A mem(10)mov A, 0xFF ;A 0xFF

mov A, 0FFH ;same as above


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Register Set B Register

l Commonly used as a temporary register, much

like a 9th R register

l Used by two opcodes

mul AB, div AB

l B register holds the second operand and will

hold part of the result

Upper 8bits of the multiplication result Remainder in case of division


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Register Set R0 to R7

l Set of 8 registers R0, R1, R7, each 8 bit wide

l Widely used as temporary registers

l Available in 4 banks (effectively 4x8 registers)

l Bank is chosen by setting RS1:RS0 bits in PSWl Default bank (at power up) is the bank0

l Examples

mov R0, A ;R0 A

mov A, R0 ;A R0mov R1, #45 ;R1 45


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Registers - DPTR

l 16 bit register, called Data Pointer

l Used by commands that access externalmemory

l Also used for storing 16bit values

mov DPTR, #data16 ; setup DPTR with 16bit ext address

movx A, @DPTR ; copy mem[DPTR] to A

l DPTR is useful for string operations, look uptable (LUT) operations


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Registers - PC

l PC is the program counter

l Referred to as the Instruction Pointer (IP) inother microprocessors

l PC points to the next program instruction

always

l After fetching an instruction (1 or multi byte),

PC is automatically incremented to point to thenext instruction


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Registers - SP

l SP is the stack pointer

l SP points to the last used location of the stack push will first increment SP and then copy data

pop will first copy data and then decrement SP

l In 8051, stack grows upwards (from low mem to highmem) and can be in the internal RAM only

l On power-up, SP is at 07H

l Register banks 2,3,4 (08H to 1FH) is the default stack

areal Stack can be relocated by setting SP to the upper

memory area in 30H to 7FH mov SP, #32H


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Registers - PSW

l Program Status Word is a bit addressable8bitregister that has all the flags

l CY - Carry Flag Set whenever there is a carry in an arithmetic operation

l AC - Aux. Carry Flag Carry from D3 to D4. Used for BCD operation

l P - Parity Flag P=1 if A has odd number of 1s

Even parityl OV - Overflow Flag

Set if any arithmetic operation causes an overflow


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Flags - Illustration

l Addition example mov A, #38

add A, #2F

38 0011 1000

+ 2F 0010 1111

--------- ---------------

67 0110 0111

--------- ---------------

CY = 0

AC = 1

P = 1


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Registers - SFRs

l Control the operationof on-boardperipherals

l Special FunctionRegisters at directaddresses 80H to FFH

l 8051 Clones may have

additional SFRsl All registers have an

address


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8051 Memory map

l Separate Code and Data memory

l Code Memory Upto 64K long (some maybe onboard) (0x0000 to 0xFFFF)

PSEN is the controlling signal

Can store Program only (Read only)

l Data Memory Upto 64K long (0x0000 to 0xFFFF)

RD/WR are the controlling signals

Can store data only (Read and Write)l Internal RAM

128 bytes 0x00 to 0x7F (includes register banks)

SFRs 0x80 to 0xFF (not all available)


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8051 - Memory Map

l Internal ROM is vendor dependant

l On power-up PC starts at 0000H inROM space

l Clones may have internal memorythat may be used as bothCode+Data

mov A, xxH

movc A,@A+DPTR

movx A, @DPTR

mov A, xxH

mov @Ri

InstructionSignalEndStartMemoryType

0xFF0x80SFRs

PSEN0xFFFF0x0000Code

RD, WR0xFFFF0x0000Data

0x7F0x00IRAM


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8051 Instruction Set

l Data Transfer Move/Copy data from one location to another

mov, movc, movx, push, pop, xch, xchd

l Logical

Perform logic operations on data anl, orl, xrl, clr, cpl, rl, rlc, rr, rrc, swap

l Arithmetic Perform arithmetic operations on data

add, addc, subb, inc, dec, mul, div

l Program control Control the program flow (jumps, subroutine calls)

jmp, ajmp, ljmp, sjmp, jc, jnc, jb, jnb, jbc, jz, jnz, acall, lcall,cjne, djnz, ret, reti

l

NOP


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8051 Instruction Set (contd.)

l Read through the instruction set

Dont have to remember all the instructions

Dont have to remember all possible cases

l Remember the types of instructions

l When writing code

Write down the operation needed in simple English

Lookup the instruction set to see which (combo) ofinstructions will do the job


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Assembly Opcode

l Every assembly instruction translates to a unique

binary Opcode

Can be 1, 2 or 3 bytes long

8051 Family Programmers Guide has a list

l Example1: mov A, #data

2 bytes, 1 cycles

0111 0100 data8

mov A, 0xAA 0111 0100 1010 10101 74 AA

l Example2: acall address11

a10 a9 a8 1 0001 a7 a6 a5 a4 a3 a2 a1 a0

acall 0x557 101 1 0001 0101 0111 B1 57


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Assembler Directives

l Assembly statement structure

[label:] opcode [operands] [;comment]

start: mov A, #D0H ;code starts here

l

Assembler directives Instruct assembler to do a specialtask

ORG xxxxH : origin, start assembling at xxxxH

EQU : define a constant

l count EQU 25

DB : define byte, defines allocation of storagel DATA1: DB 28

l DATA2: DB hello world

END : end of assembly file


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Assembly Design Flow

l Create the assembly source file test.asm

l Assemble the asm file

C:\> as51 test.asm

Assembler produces error and code list in test.lst If no errors, assembler produces .obj file

l Link the .obj files to produce an .abs file

l Create hex file from the .abs file

l Most assemblers directly produce the .hex filel Download the .hex file onto the board or burn it into an

EPROM.


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Assembly Example #1

l Target 8051 dev system

Std 8051 device

2K on-chip ROM runninga monitor program

32K external RAM ataddress 0x0000 to0x7FFF

This RAM is both codeand data

First 0x30 locations in

external RAM isdedicated for the InterruptVector Table (IVT)

l Program to fill up the first 4 registers in theregister bank with some numbers and find theirsum

ORG 0x30 ;skip the IVT area

Start: mov R0, #10

mov R1, #0A5H

mov R2, #1mov R3, #0x20

clearA: mov A, #0 ;now A = 0

Addup: add A, R0 ;now A = A + R0

add A, R1

add A, R2

add A, R3mov R4, A ;store sum in R4

mov DPTR, #7FFF

movx @DPTR, A ;store in ext. mem

Done: sjmp done ;loop here forever

END


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Class 2 Review

l What are the different views/models of a uP ?

l What are the registers available in the 8051 ?

l What are the functions of the 8051 registers ?

l What is stack, PC, SFR, PSW/Flags ?

l What is an instruction set ?

l What is a memory map ? Why is it needed ?

l What is an assembly language program ? How

does it look ?

Intro to 8051 Assembly Programming

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