8051 Microcontroller –

8/6/2019 8051 Microcontroller –

http://slidepdf.com/reader/full/8051-microcontroller- 1/20

Pari vallal Kannan

Center for Integrated Circuits and Systems

University of Texas at Dallas

8051 Microcontroller –Architecture, Intro to Assembly

Programming

EE4380 Fall 2002

Class 2



29-Aug-02 2

Class –2: Objectivel 8051 internal architecture

l Register Set

l

Instruction Setl Memory Map

l Intro to Stack, SFRs

l Assembly language programming



29-Aug-02 3

8051 Architecturel Programmer’s View

– Register Set

– Instruction Set

– Memory map

l Hardware Designer’s View

– Pinout

–

Timing characteristics – Current / Voltage requirements



29-Aug-02 4

Programmer’s View – Register Setl 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



29-Aug-02 5

Assembly – Absolute Basicsl 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

0must

precede it – #0FFH, #0C1H, #0D2H

l No operation : NOP !



29-Aug-02 6

Register Set – Accumulator A, ACCl Commonly used for mov and arithmetic

l Implicitly used in opcodes or referred to asACC or by its SFR address 0E0H

l Example of Implicit reference – Instruction : mov A, R0 (copy contents of R0 to A)

– Opcode : E8

– The Accumulator is implicitly coded in the opcode

l Explicit reference to Accumulator – Instruction : push ACC

– Opcode: C0 E0



29-Aug-02 7

Register Set – B Registerl 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



29-Aug-02 8

Register Set – R0 to R7l 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

PSW

l Default bank (at power up) is the bank0



29-Aug-02 9

Registers - DPTRl 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



29-Aug-02 10

Registers - PCl PC is the program counter

l Referred to as the Instruction Pointer (IP) in other

microprocessors

l PC points to the next program instruction always

l After fetching an instruction (1 or multi byte), PC isautomatically incremented to point to the nextinstruction

l

Cannot directly manipulate PC (exceptions JMPstatements)

l Cannot directly read contents of PC (tricks available)



29-Aug-02 11

Registers - SPl SP is the stack pointer

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

– Pop operation will first copy data and then decrement SPl In 8051, stack grows upwards (from low mem to high

mem) 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



29-Aug-02 12

Registers - PSW

l Program Status Word is a “bit addressable” 8bitregister that has all the flags

l CY - Carry Flag

– Set whenever there is a carry in an arithmetic operationl 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



29-Aug-02 13

Flags - Illustration

l Addition example

38 0011 1000

+ 2F 0010 1111

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

67 0110 0111

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

CY = 0AC = 1

P = 1



29-Aug-02 14

Registers - SFRs

l Control the operation

of on-boardperipherals

l Special Function

Registers at direct

addresses 80H to FFH

l

8051 Clones may haveadditional SFRs



29-Aug-02 15

8051 - Memory Map

l Internal ROM is vendor dependant

l On power-up PC starts at 0000H in

ROM space

MOVC

MOVC, MOVX

MOVX A, @DPTR

MOV A, xxH

InstructionSignalEndStartMemoryType

????H0000HInternal ROM

PSENFFFFH0000HExternalROM

RD,WR

FFFFH0000HExternal RAM

7FH00HInternal RAM



29-Aug-02 16

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



29-Aug-02 17

8051 Assembly Introduction

l Assembly statement structure[label:] opcode [operands] [;comment]

l Example

start: mov A, #D0H ;code starts herel Assembler directives

– ORG xxxxH : origin, start assembling at xxxxH

– EQU : define a constant

l count EQU 25

– DB : define byte, defines data

l DATA1: DB 28

l DATA2: DB “hello world”

– END : end of assembly file



29-Aug-02 18

Assembly Design Flow

l Create the assembly source file test.asm

l Assemble the asm file

– 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.



29-Aug-02 19

Assembly Example #1

l Target 8051 dev system

– Std 8051 device

– 2K on-chip ROM running

a monitor program

– 32K external RAM ataddress 0x0000 to0x7FFF

– This RAM is both code

and data

– First 0x30 locations in

external RAM isdedicated for the Interrupt

Vector 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, #1

mov 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



29-Aug-02 20

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 ?

Documents

8051 Microcontroller –