Basic Microprocessor's (Intel 4004 and 8085).

What is Microprocessor??

A microprocessor incorporates the functions of a computer processing unit (CPU) on a single integrated circuit (IC). All modern CPUs are microprocessors making the micro- prefix redundant. The microprocessor is a multipurpose,programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and provides results as output. It is an example of sequential digital logic , as it has internal memory. Microprocessors operate on numbers and symbols represented in the binary numeral system.

Block diagram of a simple microprocessor.

The integration of a whole CPU onto a single chip or on a few chips greatly reduced the cost of processing power. The integrated circuit processor was produced in large numbers by highly automated processes, so unit cost was low. Single-chip processors increase reliability as there are many fewer electrical connections to fail. As microprocessor designs get faster, the cost of manufacturing a chip (with smaller components built on a semiconductor chip the same size) generally stays the same.

A Simple microprocessor chip.

Before microprocessors, small computers had been implemented using racks of circuit boards with many medium- and small scale integrated circuits. Microprocessors integrated this into one or a few large scale  ICs. Continued increases in microprocessor capacity have since rendered other forms of computers almost completely obsolete, with one or more microprocessors used in everything from the small embedded system and handheld devices to the largest mainframes and supercomputers.

The man who invented the 

Microprocessor.

Intel employee number 12, Marcian Edward "Ted" Hoff, was recruited by Robert Noyce and led the project that created the first microprocessor.

Ted Hoff saved his own life, sort of.

Continue reading the main story

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Classification of Microprocessor-

The microprocessor is identified with the word size of data. For E.g. The ALU can perform a 4- bit data operation at a time these microprocessor is called as 4-bit microprocessor. 

4-Bit Processors

INTEL 404 4040.

8-Bit Processors

8008 8080 8085 MOTOROLA 6800 (M6800) .

16-Bit Processors

8086 8088 Zilog Z800 80186 80286 .

32-Bit Processors

Intel 80386 80387 80486 PENTIUM PENTIUM PRO .

The world's first single chip

microprocessor invented by'' INTEL''.

In November, 1971, a company called ''Intel 4004'' ("four-thousand-four") is a 4-bit central processing unit (CPU) released by Intel corporation.. ''Intel''  publicly  introduced  the  world's  first  single chip microprocessor, the Intel 

4004  (U.S. Patent #3,821,715), invented by Intel engineers  Federico Faggin,Ted hoff , and Stanley mazor . After  that  the invention of integrated circuits revolutionized computer design, the only place to go was down -- in size that is The Intel 4004 chip took the integrated circuit down one step further placing the invention of integrated circuits revolutionized computer design, the only place to go was down -- in size that is

The Intel 4004 chip took the integrated circuit down one step further by placing all the parts that made 
computer think (i.e. central processing unit, memory, input and output controls) on one small chip. Programming intelligence into inanimate objects had now become possible. 

Intel 4004 chip

The 4004 was history’s first monolithic CPU fully integrated in one small chip. Such a feat of integration was made possible by the use of the then-new silicon gate technology which allowed twice the number of random-logic transistors and an increase in speed by a factor of five compared to the incumbent technology. The 4004 microprocessor was one of 4 chips constituting the MCS-4 chip-set, which included the 4001 ROM, 4002 RAM, and 4003 Shift Register. With these components, small computers with varying amounts of memory and I/O facilities could be built. Three other CPU chip designs were done at about the same time: the Four-Phase System AL1, done in 1969; the MP944, completed in 1970 and used in the F-14 Tomcat fighter jet; and the Texas Instruments TMS0100 chip, announced in September 17, 1971. Both the AL1 and the MP944 used several chips for the implementation of the CPU function. The TMS 0100 chip, presented as a “calculator on a chip” with the designation TMS1802NC, was first used commercially in a TI calculator product introduced in 1972.This chip contained a very primitive CPU which could only implement a variety of simple 4-function calculators. It was the precursor of the TMS1000, introduced in 1974, which is considered the first microcontroller i.e., a computer on a chip containing not only the CPU, but also ROM, RAM, and I/O functions.The MCS-4 family of 4 chips developed by Intel, of which the 4004 was the CPU or microprocessor, was far more versatile and powerful than the single chip TMS1000, allowing the creation of a variety of small computers for various applications. The MCS-4 was eventually superseded by powerful microcontrollers like the Intel 8048 and the Zilog Z8 in 1978-1979.

Block diagram of Intel 4004-

Pin diagram of Intel 4004-

Intel 8085 microprocessor (The basic microprocessor)-

The Intel 8085 ("eighty-eighty-five") is an 8-bit microprocessor  introduced by Intel in 1977.It was backward binary compatible with the more-famous Intel 8080 (only adding a few minor instructions) but required less supporting hardware, thus allowing simpler and less expensive microcomputer systems to be built.

The "5" in the model number came from the fact that the 8085 requires only a +5- volt  (V) power supply by using depletion mode transistors, rather than requiring the +5 V, −5 V and +12 V supplies the 8080 needed.

 A 8085 chip.

The Intel 8085 required at least an external ROM and RAM and an 8 bit address latch (both latches combined in the Intel 8755  2Kx8 EPROM / 2x8 I/O, Intel 8155 256-byte RAM and 22 I/O and 14 bit programmable Timer/Counter) .

Architecture of 8085-

This is the functional block diagram of the 8085 Microprocessor.

Working of 8085-

Acumulator-

It is a 8-bit register which is used to perform airthmetical and logical operation. It stores the output of any operation. It also works as registers for i/o accesses. 

Temporary Register-

It is a 8-bit register which is used to hold the data on which the acumulator is computing operation. It is also called as operand register because it provides operands to ALU. 

Registers-

These are general purposes registers. Microprocessor consists 6 general purpose registers of 8-bit each named as B,C,D,E,H and L. Generally theses registers are not used for storing the data permanently. It carries the 8-bits data. These are used only during the execution of the instructions. 
These registers can also be used to carry the 16 bits data by making the pair of 2 registers. The valid register pairs available are BC,DE HL. We can not use other pairs except BC,DEand HL. These registers are programmed by user. 

ALU-

ALU performs the airthmetic operations and logical operation. 

Flag Registers-

It consists of 5 flip flop which changes its status according to the result stored in an accumulator. It is also known as status registers. It is connected to the ALU.
There are five flip-flops in the flag register are as follows:

1. Sign(S)
2. zero(z)
3. Auxiliary carry(AC)
4. Parity(P)
5. Carry(C)

Instruction registers(IR)-

It is a 8-bit register. When an instruction is fetched from memory then it is stored in this register. 

Instruction Decoder-

Instruction decoder identifies the instructions. It takes the informations from instruction register and decodes the instruction to be performed. 

Program Counter-

It is a 16 bit register used as memory pointer. It stores the memory address of the next instruction to be executed. So we can say that this register is used to sequencing the program. Generally the memory have 16 bit addresses so that it has 16 bit memory. The program counter is set to 0000H. 

Stack Pointer-

It is also a 16 bit register used as memory pointer. It points to the memory location called stack. Generally stack is a reserved portion of memory where information can be stores or taken back together. 

Timing and Control Unit-

It provides timing and control signal to the microprocessor to perform the various operation.It has three control signal. It controls all external and internal circuits. It operates with reference to clock signal.It synchronizes all the data transfers.
There are three control signal:

1. ALE-Airthmetic Latch Enable, It provides control signal to synchronize the components of microprocessor.
2. RD- This is active low used for reading operation.
3. WR-This is active low used for writing operation.

There are three status signal used in microprocessor S0, S1 and IO/M. It changes its status according the provided input to these pins. 

Serial Input Output Control-

There are two pins in this unit. This unit is used for serial data communication. 

Interrupt Unit-

There are 6 interrupt pins in this unit. Generally an external hardware is connected to these pins. These pins provide interrupt signal sent by external hardware to microprocessor and microprocessor sends acknowledgement for receiving the interrupt signal. Generally INTA is used for acknowledgement. 

Register Section-

Many registers has been used in microprocessor. PIPO shift register It consists of PIPO(Parallel Input Parallel Output) register. 

Pin diagram of 8085-

Addressing modes in 8085-

1. Immediate Addressing Mode
2. Register Addressing Mode
3. Direct Addressing Mode
4. Indirect Addressing Mode
5. Implied/implicit Addressing Mode

Immediate Addressing Mode:

An immediate is transferred directly to the register. 
Eg: -

MVI A, 30H (30H is copied into the register A)
MVI B,40H(40H is copied into the register B)

Register Addressing Mode:

Data is copied from one register to another register. 
Eg: -

MOV B, A (the content of A is copied into the register B)
MOV A, C (the content of C is copied into the register A)

Direct Addressing Mode:

Data is directly copied from the given address to the register. 
Eg: -

LDA 3000H (The content at the location 3000H is copied to the register A).

Indirect Addressing Mode:

The data is transferred from the address pointed by the data in a register to other register. 
Eg: -

MOV A, M (data is transferred from the memory location pointed by the regiser to the accumulator).

Implied Addressing Mode:

This mode doesn't require any operand. The data is specified by opcode itself. 
Eg: -

RAL
CMP

Bus structure in 8085-

There are three buses in Microprocessor:

1. Address Bus
2. Data Bus
3. Control Bus

Bus structure of 8085