Micro Processor

Posted by : Unknown Friday, July 26, 2013

MICROPROCESSOR

Introduction:

Minicomputer is making a great impact on every day activity of mankind and plays an important role in day-to-day working of industrialized societies. Large computers were designed to solve complex scientific and engineering problems and handle records of large corporations and government agencies. Only large institutions and organisations were able to purchase digital computers. A trend started in the middle of 1960’s to design smaller computers for smaller organisations. In the late 1960’s minicomputers were available for use in an office, small college, medium-sized business organizations, small factory and laboratory. The smaller organizations that were not able to afford large computer could now purchase a minicomputer.

Definition:

With the advent of Semiconductor technology, it became possible to fabricate the whole CPU of a digital Computer on a single chip using VLSI technology. A VLSI-IC contains more than 10,000 transistors. A CPU built into a single IC called a microprocessor. A digital Computer whose CPU is a microprocessor is called a microcomputer. A microprocessor combined with memory and Input / Output devices form a microcomputer.

Evolution of Microprocessor:

In 1971 Intel Corporation, U.S.A introduced the first microprocessor the Intel 4004, which was a 4-bit microprocessor. In 1972 Intel introduced the first 8-bit microprocessor, the Intel 8008. In 1973 a more powerful and faster 8-bit microprocessor, the Intel 8008 was introduced.

In 1973 second generation 8-bit microprocessors evolved. They were Intel 8080/8085, Fair Child, F-8, and Motorola 6800.

After 1978, the third generation microprocessors were introduced. These Processors are 16-bit wide and include typical processors such as Intel 8086/8088/80186/80286, Motorola 68000/68010.

Fourth generation microprocessors evolved in the year 1981. Intel introduced the first commercial 32-bit microprocessor in Intel 432. Since 1985, more 32-bit microprocessors were been introduced. These include Motorola 68020, 68030 and Intel 80386. In 1989, Intel introduced the 32-bit microprocessor Intel 80486. Later Intel has introduced 64-bit microprocessor Intel 80586(Pentium).

Microprocessor Operation:

The CPU microprocessor was digital circuits for data handling and computation under program control. That is microprocessor is a data processing unit. Data processing is the microprocessors main function. Date processing includes both computation and data handling. To do this, it must have logic, which tells the microprocessor how to decode and execute the program, and also the control logic determines which circuit to process the data. The Microprocessor operates in the following steps. First the microprocessor fetches an instruction. Then the control logic decodes what the instruction says to do. After de loading, the microprocessor executes the instruction these steps are called fetch and execute cycle for each instruction in memory the microprocessor goes through one fetch and execute cycle.

The control logic controls how the microprocessor works with all of the outside circuits (memory, input, and output) Connected to the microprocessor. Microprocessor can do nothing by itself. The microprocessor must have the aid of other circuits. Some memory circuits are required to store the program instructions and circuits are also needs to more data into and out of the Microprocessor these circuits are called input / output circuits. The micro process or also requires a power supply. The microprocessor is the heart of many products, but the microprocessor is never a complete, working product itself.

Microcomputer:

Frequently the words “microprocessor” and “microcomputer” are used to mean the same thing, but infect these similar words have different meanings. The microprocessor is an IC. It includes the circuits for two purposes, Data processing and control. But the microcomputer is a complete computing system built around a microprocessor. Some microcomputers are personnel computers and some other microcomputer systems are dedicated computational systems based on a microprocessor.

Power of a microprocessor:

Almost all microprocessors are made on silicon die (often called ICs). These ICs are about ¼ inch or 0.64 cm, on side. The measures of he power of a microprocessor are the length of a microprocessor’s data word. The number of memory words that the microprocessor can address, and the speed with which the microprocessor can execute an instruction. Microprocessors are most often compared in terms of the lengths of their data words. The microprocessor works on fixed length date word. Today the most common word lengths are 4bits 8bits, 10bits and 32 bits. Soon, 64 bit microprocessors will become common too.

Another common measure of microprocessor power is the number of memory bytes that the microprocessor can address. Here the length of data word in memory is same as the length of the data word used by the microprocessor for example a 4-bit microprocessor stores 4-bit words in memory. Each word in memory is assigned a location number or address.

The third measure of microprocessor executes an instruction. Speed is determined by the time it takes the microprocessor to complete the fetch execute cycle for one program step. This oscillator circuit is called the microprocessor’s clock slow microprocessors may use a clock that runs at a few Kilo Hertz. Such microprocessor takes 10 to 20 microseconds to execute one instruction. On the other hand some microprocessors use clocks that run at 10 to 100 MHz. These microprocessors may execute an instruction in only a few tenths of a microsecond. The microprocessor’s speed related to its maximum clock frequency.

Number System:

The microprocessor is built with digital logic and therefore manipulates binary data. We often ask the microprocessor to perform arithmetic functions often we want output and input information in the familiar decimal numbers. Therefore to use microprocessor number system plays an important role. Different number systems are

Binary
Decimal
Octal
Hexadecimal

It is possible to convert from one system to any another system.

Microprocessors Architectural Concepts:

Microprocessor's Architecture:

We know that there is no precise definition of architecture; the following examples should help to understand the architecture. We all know that the person who designs buildings is an architect. We realize that while all buildings perform similar functions, i.e. they keep whether out they do it in different ways. The same is true of microprocessors. There are many different ones. Most try to do the same job, but the internal structure that they use to do job is different. That is their architecture is different.

For some microprocessors, the architectural differences are small. For others, the differences are large. For example, the Intel 8051 8-bit single chip microprocessor and the Intel 486 32-bit microprocessor will both add two numbers. The way of adding two numbers and the parts they use to add the two numbers are quite similar. However, to compute the cosine of an angle, the way they perform this task and the parts they use will be very different. Each of them can do the job, one with great ease and another with extremely different. Since they have different architectures.

The major architectural differences between microprocessors are

The length of the microprocessor's data word.
The size of the memory, which the microprocessors can directly address.
The speed which the microprocessor can execute instructions.

Some additional architectural differences between microprocessors are:

· The number of registers available to the programmer.

· The different types of registers available to the programmer.

· The different types of instructions available to the programmer.

· The different types of memory addressing modes available to the programmer.

· The different types of circuits available to the system designer.

· Compatibility with readily available development, system and applications software.

· Compatibility with hardware development systems.

These differences make some microprocessors better for some applications and some other microprocessors better for other applications.

Word length:

The microprocessor started as a 4-bit device. It is progressed an 8-bit, a 16-bit, a 32-bit, and now a 64-bit device. To know the performance the initial step is speed - how quickly the microprocessor will perform its internal function. This tells us that a microprocessor with a longer word length will solve more problems faster. Therefore, a longer word length should give a better solution to all problems. However, to solve a variety of problem like building a simple microprocessor controlled toy, to calculate cosine of an angle, the real performance issue is cost. The 4-bit microprocessors are very good for low cost applications. Therefore, from the above reason the shorter- word length architecture is still used.

Addressable Memory:

The amount of memory that a particular microprocessor can address is also part of its architecture. Some applications require less addressable space and others require more addressable space. Depending on requirement we will select anyone from 4-bit, 8-bit, 16-bit, 32-bit, 64-bit. The 32-bit microprocessor architecture allow to address 4 GB memory.

The Microprocessor's Speed:

The speed of microprocessor to execute an instruction is often used to compare the performance of two microprocessors. Speed may be measured in two different ways. The first is the microprocessors clock speed. This is the frequently at which the microprocessor's clock oscillator operates. Typically this is expressed in megahertz (MHz). The second method of rating a microprocessor's speed is the number of instructions it can execute per second. Processing speed is usually expressed in millions of instructions per second (MIPS).

The processing rate depends on both the clock frequently and the word size. If two microprocessors perform a memory access in the same amount of time the 16-bit microprocessors will be twice as fast as the 8-bit microprocessor. The frequency at which the microprocessor's clock operates depends largely on the semiconductor manufacturing technology used to build the microprocessors. Microprocessors are constructed using one of the two semiconductor technologies. These two technologies are NMOS (N-channel metal-oxide semiconductor) and CMOS (complementary metal oxide semiconductor). CMOS processors typically will operate over a greater range than the NMOS devices.

Other Architectural Characteristics:

Some other microprocessor architectural techniques being used to increase speed included

· Parallel processing

· Co processing

· Cache memory techniques

· Pipelining techniques

· Wider buses.

Parallel processing means just what it says; this means that the microprocessor architecture permits two parts of the computing process to occur at the same time. The implementation of the parallel processing involves the use of the two microprocessors in the same product. Parallel processing is used with in the microprocessor itself. The parallel processing configuration using two microprocessors was shown below.

Advanced microprocessor architecture may include multiple execution units with in the microprocessor design. This form of parallel processing is called a super scalar architecture.

Co-processing is very much like parallel processing. The coprocessor is a separate processor, which work with the mail processor to perform special functions. Many conventional microprocessors are supported with separate IC, which perform the co-processing function. For example, the 386 are supported with the 80387 numeric data coprocessor. The 80387 are wired in parallel with the 386 processor. When combined these two processors the combined system has extra high-level mathematical performance. A 386 system using an 80387 numeric date coprocessor is shown in the following figure.

Microprocessor architecture faces speed limitation from memory read or writes. There is a technique to solve the problems is to use a very fast cache memory. This fast cache memory may locate very close to the microprocessor or it may be included with in the microprocessor on new microprocessor architectures. To offer a speed improvement the cache memory has more hits than misses.

Pipelining is another architectural technique that processes a number of instructions at one time. Each instruction is processed a little a each station just like a product is built a little at each station on an assembly line. The use of pipeline architecture allows the designer to build faster, more dedicated logic at each station and therefore the microprocessor completes the desired process quicker. When the microprocessor has the ability to process wider data it is naturally faster.

Wider data buses are used inside the microprocessor as well as in microcomputer design. We have seen examples of this architectural technique when microprocessors used doublewide accumulators. The doublewide accumulators allow processing certain functions faster because it eliminates the need to perform an intermediate storage in memory.

The Microprocessor's Registers:

The registers are temporary data storage devices found inside the microprocessors. Some has special single-purpose function and others are used for general-purpose data storage. The number and type registers in any particular microprocessor will be different from another microprocessor. The number of registers in the microprocessor is important. If the microprocessor architecture does not have enough registers to allow the programmer to assign register for a specific task, the programmer must transfer the data in the register into temporary memory locations. When the task was completed it retrieve data from temporary location to registers. The data transfer from a register to memory or memory to register is wasted instructions. The types of register available to the programmer can also represent a performance issue.

The Microprocessor's Instructions:

Like the register, the number and kind of microprocessor's instructions are a measure of the microprocessor's power. More instructions means a bigger microprocessor and bigger microprocessors are more complex.

Inside The Microprocessor:

The Microprocessor Block Diagram and Programming Model:

The microprocessor block diagram and the microprocessors programming model shows the user how the specific microprocessor is constructed. The block diagram shows a microprocessor’s logic function for data processing and data handling. It also shows how each logic function is connected to all others. The programming model shows the parts of the microprocessor that the programmer can change. The 8-bit microprocessor's block diagram is as shown below.

0 07 0

Accumulator	Status Register
Reg B	Reg C
Reg D	Reg E
Reg H	Reg L
SP
PC

The programming model only shows those registers which the programmer can use to store data or which the programmer must access to have right data for a program operation.

The ALU :

One of the microprocessors major logic functions is the arithmetic logic unit. It contains the microprocessors data processing logic. It has two input ports and one output port.

An input port is made up of logic circuits used to get a data word into a logic device. An output port is made up of logic circuits used to get out a data word out of a logic device.

Both input ports are buffered by a temporary registers. Each port has a register that temporarily stores one data word. The microprocessors internal bus is connected to the ALU`s two input ports through the temporary registers. This allows it to take data from any device on the microprocessors internal data bus. Often, the ALU gets its data from a special register called the accumulator. The ALU's single output port allows it to send a data word over the bus to any device connected to the bus. The list of ALU functions varies from one microprocessor to another.

The ALU’s of most microprocessors can perform all functions as

Add, Subtract, AND, OR, Exclusive OR, Complement,

Shift right, Shift left, Increment, Decrement.

ALU’s have many functions and others have only a few.

The Microprocessor's Registers:

Registers are an important part of the block diagram and the programming model of any microprocessor. There are different registers. The basic registers found in most microprocessors are the accumulator, the program counter, the stack pointer, the status register, the general-purpose registers, the memory address register, the instruction register and temporary data register.

Accumulator:

The accumulator is the microprocessor's major working register. For example, the microprocessor's addition of two words is first word A is placed in the accumulator. The addition is then executed by adding word B (the contents of memory location) to word A (in the accumulator). The resulting sum is placed in the accumulator, replacing word A. Another kind of operation using the accumulator is the programmed data transfer. It moves data from one place to other. Data movements between I/O port and a memory location or between one-memory locations to other memory location. The data transfer takes place in two stages i.e. the data is moved from source to accumulator and from accumulator to destination. Some microprocessors have multiple accumulators.

Program Counter:

The program counter is one of the most important registers in the microprocessor. Before the microprocessor can start executing a program, the program counter has to be loaded with a number. This number is the address of the memory location containing the first program instruction. Usually this is a simple number such as all zeros or all ones. Once the microprocessor fetches an instruction from memory, the microprocessor automatically increments the program counter. The program counter always point to the next instruction throughout the time the current instruction is being executed.

Status Register:

The register that can make the difference between a simple calculator and an arithmetic computer is the status register. The status register is used to store the results of certain tests performed during execution of a program. Some common status register bits are: carry/barrow, zero, negative, intermediate, carry, interrupt, flags, overflow, parity. If two 8 bit numbers are added and there sum is greater than 11111111 then a carry is generated. When this carry is generated, the microprocessor sets the status registers carry bit.

Stack Pointer:

The programmer require to pushes the information on to the stack in order and pops the information from the stack in the reverse order. The kind of operation on the stack is LIFO (last in first out). To do this the programmer uses a special register called the stack pointer. Like the program counter, the stack pointer automatically points to the next available pointer location. In most microprocessors, the stack pointer decrement after it is used.

General-Purpose Registers:

In addition to the size basic registers, most microprocessors have other registers for general programming use. These other registers are called general-purpose registers. The microprocessor used size general-purpose called the B, C, D, E, H, and L registers.

Instruction Register:

The instruction register holds the instruction the microprocessor is currently executing. This is instruction register’s only job, and the instruction register performs it automatically. Instruction register is important, because its output always drives the part of the control logic known as instruction decoder. During execution the instruction decoder decodes the instruction to tell the microprocessor exactly what to do to carry out the instruction. The length of the instruction register is varies from one microprocessor to another. In some microprocessors, the instruction word is as long as the data word. In others, instruction word may be as sort as 3 or 4 bits.

Temporary data registers:

The temporary registers are required because the ALU has no data storage of its own. The ALU must take data from the microprocessor’s internal data bus, change the data and then placed the change data into accumulator. The ALU ’s temporary registers cannot be used by the programmer and therefore, are not part of the programming model. These temporary registers are very essential to the internal function of the microprocessor.

Memory Address Register:

Every time microprocessor addresses the microprocessor memory, the memory address register points to the memory location the processor wants to use. During the fetch cycle an instruction is taken from memory. The memory address register points to the instruction word being fetched from memory. The memory address register must have enough bits to address any location in the microprocessor’s memory. A 16bit memory address register may be divided into two separate registers each with an independent connection to the microprocessor’s data bus. These registers are called High-byte and the Low-byte memory address registers.

Microprocessor’s Control Logic:

Another major logic function of the microprocessor is its control logic. The control logic takes instructions from the instruction register, figures out what to be done to the data and then gives the commands necessary to get the job done. The architecture of the control logic itself is much like the architecture of a very special purpose microprocessor. The control logic is like a small microprocessor with in the microprocessor. The control logic includes control lines to each of the microprocessor’s logic functions. These lines include the memory, I/O, and Read-write lines. These control lines send control signals to the external devices telling them what to do and when to do it.

The Microprocessor’s Internal Data Bus:

All internal microprocessor data transfers take place on this bus. The microprocessors internal data bus is made up of data signals. Almost all of the microprocessor’s logic devices have bi-directional communication with the internal data bus i.e. the devices can either place data on the bus or receive from the bus. The internal data bus may be connected to an external data bus when the microprocessor needs to send or receive data.

8086 FAMILY ASSEMBLY LANGUAGE PROGRAMMING:

Introduction to programming the 8086:

There are three language levels that can be used to write a program for microcomputer.

Machine language:

Programs as simply a sequence of the binary codes for the instructions to execute on microcomputer. This binary form of the program is referred to as the machine language, because it is the form required by the machine. It is difficult for a programmer to memorise the thousands of binary instruction codes for a CPU such as an 8086. Also it is very easy for an error to occur when working with long series of 1’s and 0’s. Using hexadecimal representation for the binary codes might help some, but still there are thousands of instruction codes.

Assembly language:

To make programming easier, many programmers write programs in assembly language. To convert the assembly language program to machine language it can be loaded into memory and run. Assembly language uses two, three, or four letter mnemonics to represent each instruction. Assembly language statements are usually written in a standard form that has four fields as shown below.

LABEL FIELD	OP CODE FIELD	OPERAND FIELD	COMMENT FIELD
NEXT:	ADD	AL, 07H	; ADD A FACTOR

The first field in the assembly language is the LABEL FIELD. A LABEL FIELD is a symbol or group of symbols used to represent an address, which is not specifically known at the time the statement written labels are used followed by a colon. It is optional field.

The OPCODE field of instruction contains the mnemonic for the instruction to be performed. Instruction mnemonics are some times called operation codes or opcodes.

The OPERAND FIELD of the statement contains the data, memory address, the port address or the name of the register. In the above example the result of ADD will put in the register or memory location specified before the comma in the operand field.

The final field in the assembly language statement is the COMMENT FILED, which is started with semicolon.

High level languages:

Another way of writing a program for a microcomputer is with a high-level language, such as BASIC, Pascal or C. The high-level language statement may represent many machine code instructions. An interpreter program or compiler program is used to translate higher language statements to machine codes, which can be loaded into the memory and executed. Writing programs in high level language is simple because the high level language works with bigger building block programs written in high level language and interpreted or compiled almost always execute more slowly and require more memory than the same programs written in assembly language. Programs that involve a lot of hard ware control, such as robots and factory control systems, or programs that must run as quickly as possible are usually best written in assembly language. Complex data processing programs that manipulate more data such as insurance company records are usually written in high-level language.

Assembly Language Program Development Tools:

The assembly language programs require some type of microcomputer development system and development tools to make easier. A typical system might consist of an IBM PC-type microcomputer with at least several hundred kilobytes of RAM, a keyword and video display, floppy and/or hard disk drives.

Editor:

An editor is a program, which allows creating a file containing the assembly language statements for a program. Writing programs on editor are called source programs. The source programs are started with an extension ASM.

Assembler:

The assembler generates two files: the first file called object is given the extension. OBJ. The object file contains the binary codes for the instructions and information about the addresses of the instructions. After further processing, the contents of this file will be loaded into memory and run. The second file generated by the assembler is called the assembler list file and is given the extension .LST.

Linker:

A linker is a program used to join several object files into one large object file. When writing large programs, it is usually much more efficient to divide the large program into smaller modules. Each module can be individually written, tested and debugged. Then, when all the modules work, their object modules can be linked together to form a large functioning program.

The linker produces a link file, which contains the binary codes for all the combined modules. The linker also produces a link map file, which contains the address information about the linked files.

Locator is a program called EXE2BIN comes with the IBM PC DOS. EXE2BIN converts a .EXE file to a .BIN file which has physical address.

A debugger is a program, which allows you to load your object code program into system memory, execute the program and troubleshoot or “debug” it.

Another way to run program is with an emulator. An emulator is a mixture of hardware and software. It is usually used to test and debug the hardware and software of external system, such as the prototype of microprocessor-based instrument.

Data Transfer Instructions:

General purpose byte or word transfer instructions:

MOV Copy byte or word from specified source to specified destination.

PUSH Copy specified word to top of stack.

POP Copy word from top of stack to specified location.

PUSHA (80186/80188 only) Copy all registers to stack.

POPA (80186/80188 only) Copy words from stack to all registers.

XCHG Exchange bytes or words.

XLAT Translate a byte in AL using a table in memory.

Simple input and output port transfer instructions:

IN Copy a byte or word from specified port to accumulator.

OUT Copy a byte or word from accumulator to specified port.

Special address transfer instructions:

LEA Load effective address of operand into specified register.

LDS Load DS register and other specified register from memory.

Flag transfer instructions:

LAHF Load AH with the low byte of the flag register.

PUSHF Copy flag register to top of stack.

Arithmetic instructions:

ADD Add specified byte-to-byte or specified word to word.

INC Increment specified byte or specified word by 1.

SUB Subtract byte from byte or word from word.

DEC Decrement specified byte or specified word by 1.

CMP Compare two specified bytes or words.

MUL Multiply unsigned byte-by-byte or word-by-word.

IMUL Multiply signed byte-by-byte or word-by-word.

DIV Divide unsigned word by byte or unsigned double word by

word.

IDIV Divide signed word by byte or unsigned double word by word.

Bit manipulation instructions:

NOT Invert each bit of a byte or word.

AND AND each bit in a byte or word with the corresponding bit in

another byte or word.

OR OR each bit in a byte or word with the corresponding bit in

another byte or word.

XOR Exclusive OR each bit in a byte or word with the corresponding bit in another byte or word.

another byte or word.

SHL Shift bits of word or byte left, put zero in LSB.

SHR Shift bits of word or byte right, put zero in MSB.

Program execution transfer instructions:

CALL Call a procedure save return address on stack.

RET Return from procedure to calling program.

JMP Go to specified address to get next instruction.

LOOP Loop through a sequence of instructions until CX=0.

INT Interrupt program execution OF=1.

IRET Return from interrupts service procedure to main program.

ENTER (80186/80188 only) Enter procedure.

LEAVE (80186/80188 only) Leave procedure.

BOUND (80186/80188 only) Check if effective address with in

specified array bounds.

TEST Wait until signal on the TEST pin is slow.

Program Format:

To write the program in correct format, assembly language coding sheets are available. The format is as follows.

ADDRESS	DATA (or) CODE	LABELS	MNEM	OPERANDS	COMMENTS

The ADDRESS column is used for the address or offset of a code byte or data byte. The actual code bytes or data bytes are put in the DATA/CODE column. A label is a name which represents an address referred to in a jump or call instruction; labels are put in the LABELS column. The MNEM column contains the opcode mnemonics for the instructions. The OPERAND (S) column contains registers, memory locations, or data acted upon by the instructions. A COMMENTS column gives you space to describe the function of the instruction for future reference.

The 8086 unconditional jump instruction:

The 8086 JMP instruction always causes a jump to occur, so this is referred to as an unconditional jump.

Example:

CODE SEGMENT

ASSUME CS: CODE

BACK: ADD AL, 03H

NOP; Dummy instruction

NOP

JMP BACK

CODE ENDS

END

The 8086 Conditional Flags:

The 8086 have 6 conditional flags. They are the carry flag (CF), the parity flag (PF), the auxiliary flag (AF), the zero flag (ZF), the sign flag (SF), and the overflow flag (OF).

If the addition of two 8-bit numbers produces a sum greater than 8-bits, the carry flag will be set to 1. Parity is a term used to indicate weather a binary word has an even number of 1's or an odd number of 1's. A binary number with an even number of 1's is said to have even parity. A binary number with an even number of 1's is said to have even parity. A binary number with an odd number of 1's is said to have odd parity. This flag has significance in BCD addition or subtraction. As the name implies zero flag will be set to 1 if the result of an arithmetic or logic operation is zero. The sign flag is used to indicate the number sign. A 0 in this bit indicates positive and 1 indicates negative. The overflow flag will be set if the result of a signed operation is too large to fit in the number of bits available to represent it.

The 8086 Conditional Jump Instructions:

The 8086 conditional jump instructions are given below.

MNEMONIC CONDITION TESTED JUMP IF...

JA/JNBE (CF or ZF)=0 above/not below nor equal

JAE/JNB CF=0 above or equal/not below

JB/JNAE CF=1 below/not above nor equal

JBE/JNA (CF OF ZF)=1 below or equal/not above

JC CF=1 carry

JE/JZ ZF=1 equal/zero

JG/JNLE ((SF xor OF) or ZF)=0 greater/not less nor equal

JGE/JNL (SF xor OF)=0 greater or equal/not less

JL/JNGE (SF xor OF)=1 less/not greater nor equal

JLE/JNG ((SF xor OF) or ZF)=1 less or equal/not greater

JNC CF=0 not carry

JNE/JNZ ZF=0 not equal/not zero

JNO OF=0 not overflow

JNP/JPO PF=0 not parity/parity odd

JNS SF=0 not sign

JO OF=1 overflow

JP/JPE PF=1 parity/parity equal

JS SF=1 sign

IF-THEN Structure:

The simple IF-THEN is implemented with a conditional jump instruction.

Example: CMP AX, BX; compare to set flags

JE THREE ; if equals then skip

ADD AX, 0002H ; add a factor

THREE: MOV CL, 07H

IF-THEN-ELSE Structure:

The IF-THEN-ELSE Structure is used to indicate a choice between two alternative courses of action.

Example: 1. CMP AL, 30 ; compare AL, 30

JB YELLOW ; if AL < 30 then YELLOW

JMP GREEN ; else GREEN

YELLOW: AL, 04H

--------

GREEN: MOV AL, 03H

--------

Example: 2 CMP AL, 30 ; compare AL, 30

JB YELLOW ; if AL < 30 then YELLOW

CMP AL, 40 ; else compare AL, 40

JB GREEN ; if AL<40 then GREEN

RED: MOV AL, 04H ; else AL > 40

-------

YELLOW: AL, 05H

--------

GREEN : MOV AL, 03H

--------

WHILE-DO LOOP:

In this loop the condition is checked before any action is done.
Example: TEMP_IN: MOV DX, 0FFF8H

IN AL, DX

CMP AL, 100

JB HEATER_ON

JMP HEATER_OFF

HEATER_ON: MOV AL, 80H

MOV DX, 0FFFAH

OUT DX, AL

JMP TEMP_IN ; while AL < 100 repeat once again

REPEAT-UNTIL Statement:

In this statement the condition is checked after any action is done.

Example: LEA BX, PRICE ; initialise pointer

MOV CX, 0008H ; initialise counter

DO_NEXT:MOV AL, [BX]

ADD AL, 03H

MOV [BX], AL

INC BX ; point to next price

DEC CX ; decrement counter

JNZ DO _NEXT ; if not last repeat once

LOOP Statement:

The LOOP statement is used to repeat the execution of instructions.

Example: MOV CX, 10

NEXT_TIME:

---------

LOOP NEXT_TIME ; this loop execute 10 times

8086 STRING Instructions:

A string is a series of bytes or words stored in successive memory locations. 8086 move a string using a MOVS instruction. To compare two strings we can use CMPS instruction. The SCAS instruction can be used to search a string to see weather it contains a specified character.

/* The comparison of two strings password program is as follows.

DATA SEGMENT

PASSWORD DB 'FAILSAFE' ; password

STR_LEN EQU ($ - PASSWPRD) ; compute length of string

INPUT_WORD DB 8 DUP (0) ;space for user password input */

PROCEDURES and MACROS:

When ever we need to use a group of instructions several times through out a program, there are two ways we can avoid having to write the group of instructions each time we want to use it. One way is to write the group of instructions as a separate procedure we can then just call a procedure whenever we need to execute that group of instructions. The CALL instruction is used to send to the starting address of the procedure in memory. A RET instruction at the end of the procedure returns execution to the next instruction in the mainline. A big advantage of using a procedure is that the machine codes for a group of instructions in the procedure only have to be put in memory once. Disadvantage of using a procedure are the need for a stack, and the overhead time required to call the procedure and return to the calling program.

When the repeated group of instructions is too short or not appropriate to be written as a procedure, we use a macro. A macro is a group of instructions we bracket and give a name to at the start of our program, the assembler will insert the defined group of instructions in place of the “Call”. Replacing the macro with the instructions it represents is commonly called “expanding” the macro. Therefore using a macro avoids the overhead time involved in calling and returning from a procedure. A disadvantage is generating in-line code each time a macro is called will make the program take memory than using a procedure. A macro to save all registers as follows.

PUSH_ALL MACRO

PUSHF

PUSH AX

PUSH BX

PUSH CX

PUSH DX

PUSH BP

PUSH SI

PUSH DI

PUSH DS

PUSH ES

PUSH SS

ENDM

Applications of microprocessors:

We will frequently find the 4-bit microprocessors are in

· Toys: robots, remote-controlled cars

· Calculators: financial, scientific, database.

· Power toll controllers: speed controls, sequencers, and measurement

devices.

· Computer peripherals: keyboard scanners, simple printers, and clocks.

· Others: refrigerator etc.

Some applications that use 8-bit microprocessors are programmable robots, video displays, light-speed printers, modems, plotters, disk controller etc. The 16-bit, 32-bit and 64-bit microprocessors have found one high-volume application and a number of low-volume applications. They are the heart of the personnel computers. The CAD (computer aided design) and CAM (computer aided manufacturing) application require 32-bit microprocessors. The microcomputer applications are slower down by the time that the 32-bit microprocessors take to get data from external devices, a 64-bit microprocessors becomes a real solution.

Conclusion:

Microprocessor is the outcome of the trend towards computer era.

Now a days they play an important role in many systems. They are used in many computer-based systems and also in many homes need goods. The microprocessors are available with both high and low speeds. Some systems require less speed and some others require high-speed microprocessors. Thus microprocessor plays important role in applications.

Assembly language plays an important role for some applications. The applications that require execution in less time are developed using Assembly language.