Microprocessor History and Generation of Microprocessor
- Fairchild semiconductors (founded in 1957) invented the first Integrated Circuit in 1959 that marked the microprocessor history. In 1968, Gordan Moore, Robert Noyce, and Andrew Grove resigned from the Fair child semiconductors and started their own company: Integrated Electronics (Intel). In 1971, the first microprocessor Intel 4004 was invented. A microprocessor is also known as a central processing unit in which numbers of peripherals’ are fabricated on a single chip. It has ALU (arithmetic and logic unit), a control unit, registers, bus systems, and a clock to perform computational tasks.
Architecture of Microprocessor
The microprocessor is a single IC package in which several useful functions are integrated and fabricated on a single silicon semiconductor chip. Its architecture consists of a central processing unit, memory modules, a system bus, and an input/output unit.
Generation of Microprocessor
2nd Generation: This was the period from 1973 to 1978 in which very efficient 8-bit microprocessors were implemented like Motorola 6800 and 6801, INTEL-8085 and Zilog’s-Z80, which were among the most popular ones. Owing to their super fast speed, they were costly as they were based on NMOS technology fabrications.
3rd Generation: During this period 16-bit processors were created and designed using HMOS technology. From 1979 to 1980, INTEL 8086/80186/80286 and Motorola 68000 and 68010 were developed. Speeds of those processors were four times better than the 2nd generation processors.
4th Generation: From 1981 to 1995 this generation developed 32-bit microprocessors by using HCMOS fabrication. INTEL-80386 and Motorola’s 68020/68030 were the popular processors.
5th Generation: From 1995 to until now this generation has been bringing out high-performance and high-speed processors that make use of 64-bit processors. Such processors include Pentium, Celeron, Dual and Quad-core processors.
Intel Celeron
It refers to a range of Intel’s X86 CPUs for value personal computer. It is based on Pentium 2 and can run on all IA-32 computer programs.
Pentium
- Pentium was introduced on March 2, in 1993. Pentium succeeded the Intel 486; The 4 indicates the fourth generation microarchitecture in the microprocessor’s history. Pentium refers to an Intel’s single-core x 86 microprocessor, which is based on the fifth-generation micro-architecture. This processor’s name was derived from the Greek word Penta, means five.
- The original Pentium processor was succeeded by the Pentium MMX in 1996. This processor has a data bus of 64 bits. A standard single transfer cycle can read or write up to 64 bits at a time. The Burst read and writes back cycles are supported by the Pentium processors. These cycles are used for cache operations and transfer 32 bytes (size of the Pentium cache line) in 4 clocks. All cache operations are burst cycles for the Pentium.
Xeon processor is a 400 MHz Pentium processor from the Intel for use in workstations and enterprise servers.
I/O Interfacing
- There are various communication devices like the keyboard, mouse, printer, etc. So, we need to interface the keyboard and other devices with the microprocessor by using latches and buffers.
Block Diagram of Memory and I/O Interfacing
8085 Interfacing Pins
- A15 – A8 (Higher Address Bus)
- AD7 – AD0(Lower Address/Data Bus)
- ALE
- RD
- WR
- READY
Internal architecture of 8085 microprocessor
- To work with microprocessor 8085, first we have to know the internal architecture of 8085 microprocessor. Internal architecture of 8085 microprocessor tells us the relation between different working blocks of 8085 microprocessor. Generally microprocessor consists of different working units those are
- Control unit: It control complete operations of microprocessor.
- ALU: It performs data processing function in respect of arithmetic and logical manner.
- Registers: It provide internal storage to CPU.
- Interrupts: It maintain priority of process.
- Internal data bus: It use to transfer data to appropriate place.
In bellow I shown the block diagram of internal architecture of 8085 microprocessor.
Now come to brief discussion on all individual units of internal architecture of 8085 microprocessor.
The ALU:
- The ALU stands for arithmetic and logical unit. As name suggest all the arithmetic and logical operation of microprocessor done inside this unit. In addition to the arithmetic & logic circuits, the ALU includes the accumulator, which is part of every arithmetic & logic operation. Also, the ALU includes a temporary register used for holding data temporarily during the execution of the operation. This temporary register is not accessible by the programmer.
Registers:
- Register is a very vital unit in internal architecture of 8085 microprocessor.
- General Purpose Registers
- Special Purpose Registers.
- Temporary Registers.
General Purpose Registers are by name B, C, D, E, H& L. All are 8 bit registers.
Special Purpose Registers:
In 8085 microprocessor there have lots of special purpose register which have specific task. In bellow you find those special purpose register.
Accumulator (8 bit register):
Accumulator is very important register in 8085 microprocessor. It store 8 bit data in size. All arithmetic and logical operation done inside the accumulator and after execution store the result of an operation. It also used to store 8 bit data during I/O transfer.
Flag Register:
Flag is a brain of a microprocessor. It is an 8 bit register. It shows the status of the microprocessor before and after an operation. In 8085 microprocessor have five flags those are S (sign flag), Z (zero flag), AC (auxiliary carry flag), P (parity flag) & CY (carry flag).
Program Counter (PC):
Program counter is also a special purpose register.This register always holds the address of the next instruction. Since it holds an address so it must be a 16 bits register.
Microprocessor 8085 Pin Configuration
Fig. 1: Block Diagram of Intel 8086
Features of 8086 Microprocessor:
- Intel 8086 was launched in 1978.
- It was the first 16-bit microprocessor.
- This microprocessor had major improvement over the execution speed of 8085.
- It is available as 40-pin Dual-Inline-Package (DIP).
- It is available in three versions:
- 8086 (5 MHz)
- 8086-2 (8 MHz)
- 8086-1 (10 MHz)
- It consists of 29,000 transistors.
Bus Interface Unit (BIU)
- Fetch the instruction or data from memory.
- Write the data to memory.
- Write the data to the port.
- Read data from the port.
Instruction Queue
- To increase the execution speed, BIU fetches as many as six instruction bytes ahead to time from memory.
- This pre fetching operation of BIU may be in parallel with execution operation of EU, which improves the speed execution of the instruction.
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Execution Unit (EU)
The functions of execution unit are:
- To tell BIU where to fetch the instructions or data from.
- To decode the instructions.
- To execute the instructions.
The EU contains the control circuitry to perform various internal operations. A decoder in EU decodes the instruction fetched memory to generate different internal or external control signals required to perform the operation. EU has 16-bit ALU, which can perform arithmetic and logical operations on 8-bit as well as 16-bit.
Fig. 2: Memory Segments of 8086
Flag Registers of 8086
Flag register in EU is of 16-bit and is shown in fig. 3:
Fig. 3: Flag Register of 8086
Flags Register determines the current state of the processor.
- Conditional Flags
- Control Flags