4-instruction-set-8051

8/7/2019 4-instruction-set-8051

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8051 MicrocontrollerAssembly Language Programming

Vaibhav V. Godbole

Lecturer, Dept. of IT


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Objective

8051 internal architecture

Register Set

Instruction SetMemory Map

Intro to Stack, SFRs

Assembly language programming

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8051 Architecture

Programmers View

Register Set

Instruction Set

Memory map

Hardware Designers View

Pinout

Timing characteristicsCurrent / Voltage requirements

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Programmers View Register Set

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

P

SW :P

rogram Status Word (a.k.a Flags)SFR : Special Function Registers

Control the on-board peripherals

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Assembly Absolute Basics

Intel Assembly format

Operation destination source ; comment

Values are to be preceded by a # sign

#55, #32 etc

Hex values are to be followed by H

#55H, #32H

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

#0FFH, #0C1H, #0D2H

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Register Set Accumulator A, ACC

Commonly used for moving data around, logic

and arithmetic operations on 8bit data

Examples

mov A, R0

push ACC

mov A, #10

mov B, A

mov A, 10mov A, 0xFF

mov A, 0FFH

21-Jan-03

;copy contents of R0 to A

;store A onto stack

;A 10

;B A

;A mem(10);A 0xFF

;same as above

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Register Set B Register

Commonly used as a temporary register, much

like a 9th R register

Used by two opcodes

mul AB, div AB

B register holds the second operand and will

hold part of the result

Upper8bits of the multiplication resultRemainder in case of division

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Register Set R0 to R7

Set of8 registers R0, R1, R7, each 8 bit wide

Widely used as temporary registers

Available in 4 banks (effectively 4x8 registers)

Bank is chosen by setting RS1:RS0 bits in PSW

Default bank (at power up) is the bank0

Examples

mov R0, A

mov A, R0

mov R1, #45

;R0A

;A R0

;R145

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Registers - DPTR

16 bit register, called Data Pointer

Used by commands that access external

memory

Also used for storing 16bit values

mov DPTR, #data16

movx A, @DPTR

; setup DPTR with 16bit ext address

; copy mem[DPTR] to A

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

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Registers - PC

PC is the program counter

Referred to as the Instruction Pointer (IP) in

other microprocessors

PC points to the next program instruction

always

After fetching an instruction (1 or multi byte),

PC is automatically incremented to point to thenext instruction

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Registers - SP

SP is the stack pointer

SP points to the last used location of the stackpush will first increment SP and then copy data

pop will first copy data and then decrement SP

In 8051, stack grows upwards (from low mem to high

mem) and can be in the internal RAM only

On power-up, SP is at 07H

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

areaStack can be relocated by setting SP to the uppermemory area in 30H to 7FH

mov SP, #32H

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Registers - PSW

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

CY - Carry Flag

Set whenever there is a carry in an arithmetic operation

AC - Aux. Carry Flag

Carry from D3 to D4. Used for BCD operation

P- Parity Flag

P=1 if A has odd number of1s

Even parityOV - Overflow Flag

Set if any arithmetic operation causes an overflow

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Flags - Illustration

Addition example

mov A, #38

add A, #2F

38

+ 2F

---------

67

---------

CY =0

AC =1

P =1

00111000

00101111

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

01100111

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

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Registers - SFRs

Control the operation

of on-boardperipherals

Special FunctionRegisters at directaddresses 80H to FFH

8051 Clones may have

additional SFRsAll registers have anaddress

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8051 Memory map

Separate Code and Data memory

Code MemoryUpto 64K long (some maybe onboard) (0x0000 to 0xFFFF)

PSEN is the controlling signal

Can store Program only (Read only)

Data Memory

Upto 64K long (0x0000 to 0xFFFF)

RD/WR are the controlling signals

Can store data only (Read and Write)Internal RAM

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

SFRs 0x80 to 0xFF (not all available)

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8051 - Memory Map

Memory Start End Signal Instruction

Type

IRAM 0x00 0x7F mov A, xxH

mov @Ri

Data

Code

SFRs

0x0000

0x0000

0x80

0xFFFF

0xFFFF

0xFF

RD, WR

PSEN

movx A, @DPTR

movc A,@A+DPTR

mov A, xxH

Internal ROM is vendor dependant

On power-up PC starts at 0000H inROM space

Clones may have internal memory

that may be used as bothCode+Data

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8051 Instruction Set

Data Transfer

Move/Copy data from one location to another

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

Logical

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

Arithmetic

Perform arithmetic operations on data

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

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

NOP

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8051 Instruction Set (contd.)

Read through the instruction set

Dont have to remember all the instructions

Dont have to remember all possible cases

Remember the types of instructions

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 Op-code

Every assembly instruction translates to a unique

binary Opcode

Can be 1, 2 or 3 bytes long

8051Family

P

rogrammers Guide has a listExample1: mov A, #data

2 bytes, 1 cycles

01110100 data8

mov A, 0xAA 0111010010101010174 AA

Example2: acall address11

a10 a9 a810001 a7 a6 a5 a4 a3 a2 a1 a0

acall 0x557 1011000101010111B157

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Assembler Directives

Assembly statement structure

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

start: mov A, #D0H ;code starts here

Assembler directives Instruct assembler to do a specialtask

ORG xxxxH

EQU

count EQU 25

: origin, start assembling at xxxxH

: define a constant

DB : define byte, defines allocation of storage

DATA1:

DATA2:

DB

DB

28

hello world

END : end of assembly file

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Assembly Design Flow

Create the assembly source file test.asm

Assemble the asm file

C:\> as51 test.asm

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

Link the .obj files to produce an .abs file

Create hex file from the .abs file

Most assemblers directly produce the .hex fileDownload the .hex file onto the board or burn it into anEPROM.

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Assembly Example #1Program to fill up the first 4 registers in the

Target 8051 dev system

Std 8051 device

2K on-chip ROM running

register bank with some numbers and find their

sum

ORG 0x30 ;skip the IVT area

a monitor program

32K external RAM ataddress 0x0000 to

0x7FFF

This RAM is both code

Start:

clearA:

Addup:

mov R0, #10

mov R1, #0A5H

mov R2, #1

mov R3, #0x20

mov A, #0 ;now A =0

add A, R0 ;now A = A + R0

and data

First 0x30 locations in

external RAM isdedicated for the Interrupt

Vector Table (IVT)

Done:

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

sjmp done ;loop here forever

END

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Class 2 Review

What are the different views/models of a uP ?

What are the registers available in the 8051 ?

What are the functions of the8051

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

What is an instruction set ?

What is a memory map ? Why is it needed ?

What is an assembly language program ? How

does it look ?

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