103: UNIT-I INTRODUCTION TO MICROPROCESSOR/MICROCOMPUTEROVERVIEW OF MICROCOMPUTER STRUCTURE AND OPERATIONA Microcomputer is a computer which is build around a microprocessor i.e whosecentral processing unit is a microprocessor. The architecture of a micro-computer systemis the layout of its major components,their principal features and their interconnectionsetc..The various units of a microcomputer system are (i) CPU (ii) Memory ,both primaryand secondary (iii) input and output devices i.e I /O devices etc..The various parts of themicrocomputer are connected by the parallel lines called buses.The three importantbuses of the microcomputer system are (a) Data bus (b) Address bus (c) Control bus.Among the three, the data bus and the control buses are bi-directional and the addressbus is an unidirectional bus.The block diagram of a simple Microcomputer system is shown below in Fig.1. Fig.1.Block Diagram of a Microcomputer system.Let us consider in detail the various blocks of the microcomputer system.MEMORY: This section of memory consists of both primary memory and secondarymemory.The primary memory constitutes the RAM & ROM. These are semiconductormemories. In addition to this ,the system may also contain secondary memories likemagnetic floppy disks, magnetic hard disks or optical disks. The memory can store the
binary codes for the sequences of instructions and also the binary coded data with whichthe computer is going to work.INPUT/OUTPUT: The I/O section allows to input the data in to the computer and sendsthe data to the outside world after necessary processing. The peripherals such askeyboards, video display terminals, printers and modems are considered as I/O devices.These devices allow the user and the computer to communicate with each other. Theactual electronic circuitary used to interface the computer buses to external devices areoften called ports. The input port allows data from a keyboard, to be read in to thecomputer under the control of CPU. An O/P Port is used to send data from the computerto some peripheral like display terminal, a printer, or a D/A converter etc..In practice,the ports of a computer is nothing but a set of D-flip-flops.CENTRAL PROCESSING UNIT : All the operations of the computer are performedunder the control of the central processing unit(CPU). The CPU fetches binary codedinstructions from memory, decodes the instructions into a series of simple actions andexecutes these actions in a sequence of steps. The CPU also contains an address counteror instruction pointer register which holds the address of the next instruction, to beexecuted . The CPU contains certain general purpose registers (GPRs) which are used fortemporary storage of binary data and also contains the control circuitry which generatesthe control bus signals.The system bus of the microcomputer constitutes three buses .They are Address bus,Databus and control bus.ADDRESS BUS : The address bus consists of 16,20,24,32 parallel signal lines. On theselines the CPU sends out the address of the memory location. If the CPU has N addresslines then it can directly address 2N memory locations.For example with 16 bit addressbus the CPU can address a memory space of 216 = 64 kB(65,536)DATA BUS- The data bus consists of 8, 16, or 32 parallel signal lines. The data bus is abi-directional bus.The double ended arrows on the data bus indicates that the CPU canread data in from memory or from a port on these lines, or it can send data out to memory
or to a port on these lines. Any device connected to this data bus must have tri-stateoutputs so that its outputs can be disabled when it is not being used.CONTROL BUS- The control bus which is also bi-directional ,consists of 4 to 10parallel signal lines. The CPU sends out signals on the control bus to enable the outputsof addressed memory devices or port devices. Typical control bus signals are memoryread, memory write, I/O read, and I/O write. To read a byte of data from a memorylocation, the CPU sends out the memory address of the desired byte on the address busand then sends out the memory read signal on the control bus. The memory read signalenables the addressed memory device to output a data word on to the data bus. The dataword from the memory travels along the data bus to the CPU.OPERATION: The operation of the microcomputer system can be explained broadly inthe following steps.(a).The microcomputer fetches each program instruction in sequence ,decodes it and thenexecutes the instruction.(b)The CPU of the microcomputer fetches instructions or reads data from memory bysending out an address on the address bus and memory read signal on the control bus.The memory outputs the addressed instruction or data word to the CPU on the data bus.(c).The CPU of the microcomputer fetches instructions or read data from memory bysending out an address on the address bus and a memory read signal on the control bus.The memory outputs the addressed instruction or data to the CPU on the data bus.(d).The CPU writes data word to memory by sending out an address on the addressbus ,and sending the data on the data bus and sending a memory write signal to memoryon the control bus.(e)To read the data from a port the CPU sends out the port address on the address busand sends an I/O read signal to the port device on the control bus.The data from the portcomes into the CPU on the data bus.
(f). To write data to a port ,the CPU sends out the port address on the address bus ,alsosends the data to be written to the port on the data bus and sends an I/O write signal to theport device on the control bus.IDEAL MICROPROCESSOR: An ideal microprocessor is only a hypothetical devicewhich contains the complete set of input, out lines ,memory and all the other necessaryports on the same chip. The internal ROM stores the sequence of instructions known asprogram in the binary code. The input signals are applied at the input pins and areprocessed according to the instructions of the program and the output in the binary shouldbe available at the output pins. The m input and n output ideal microprocessor with internal ROM isshown in the figure below. Fig 2.Ideal MicroprocessorThe concept of ideal microprocessor is not practically possible due to many constraints.For example,in a 8085 microprocessor there are 8 data lines and 16 address lines .So ,tofabricate an ideal 8085 microprocessor one has to use 8-pins for data and 16-pins foraddress lines.If this is followed ,the total number of pins increases drastically as a resultof which the size and complexity and also the cost of the IC increases. Also it is notpossible to provide large amount of on chip memory and large number of I/O ports. So,inall practical or real microprocessors ,using the multiplexing concept the number of I/Opins is reduced and also small amount of memory is introduced so that both the size and
the cost of the processor reduces. A programmable peripheral interface is used for I/Oports. This will reduce the size and cost of the microprocessor. Due to the above said reasons, the concept of ideal microprocessor isonly a hypothetical and not practically possible.MICROPROCESSOR EVOLUTION AND TYPES:EVOLUTION : The first Microprocessor (4004) was designed by Intel Corporation which wasfounded by Moore and Noyce in 1968. In the early years, Intel focused on developingsemiconductor memories (DRAMs and EPROMs) for digital computers. In 1969, aJapanese Calculator manufacturer, Busicom approached Intel with a design for a smallcalculator which need 12 custom chips. Ted Hoff, an Intel Engineer thought that ageneral purpose logic device could replace the multiple components. This idea led to thedevelopment of the first so called microprocessor. So, Microprocessors started with amodest beginning of drivers for calculators. Fedrico Faggin and Stanely Mazorimplemented the ideas of Ted Hoff’s and designed the Intel 4000 family of processorscomprising 4001 (2K-ROM), the 4002 (320 bit RAM), the 4003 (10 bit I/O shift-register)and the 4004, a 4 bit CPU. Intel introduced the 4004 microprocessor to the world widemarket on November 15, 1971. It was a 4-bit PMOS chip with 2300 transistors. Aroundthe same time Texas Instruments developed a 4-bit microprocessor TMS 1000 andbecame the owner of microprocessor patent. Later Intel introduced world’s first 8 bitgeneral purpose microprocessor 8008 in 1972. This processor was used in the popularcomputer ‘Mark-8’ in those days. In 1974, Intel introduced the improved version of8008, the 8080 microprocessor. This 8080 is the much more highly integrated chip thanits predecessors which is built around N-channel MOS technology. It could execute up to290,000 operations per second and could address up to 64K.bytes of memory. During thesame time Motorola introduced the 8-bit microprocessor Motorola 6800, and RockwellPPS-8 and Signetics 2650 with powerful architecture and instruction set. With developments in integration technology Intel was able to integrate theadditional chips like 8224 clock generator and the 8228 system controller along with
8080 microprocessor with in a single chip and released the 8 bit microprocessor 8085 inthe year 1976. The 8085 microprocessor consisted of 6500 MOS transistors and couldwork at clock frequencies of 3-5 MHz. It works on a single +5 volts supply. The otherimproved 8 bit microprocessors from the Motorola company is MC 6809,from ZILOGcompany is Zilog Z-80 and from RCA is COSMAC. In 1978, Intel introduced the 16 bit microprocessor 8086 and 8088 in 1979.IBM selected the Intel 8088 for their personal computer (IBM-PC).8086 microprocessormade up of 29,000 MOS transistors and could work at a clock speed of 5-10 MHz. It hasa 16-bit ALU with 16-bit data bus and 20-bit address bus. It can address up to 1MB ofaddress space. The pipelining concept was used for the first time to improve the speed ofthe processor. It had a pre-fetch queue of 6 instructions where in the instructions to beexecuted were fetched during the execution of an instruction. It means 8086 architecturesupports parallel processing. The 8088 microprocessor is similar to 8086 processor inarchitecture ,but the basic difference is it has only 8-bit data bus even though the ALU isof 16-bit.It has a pre-fetch queue of 4-instructions only. In 1982 Intel released another 16-bit processor called 80186 designed by ateam under the leadership of Dave Stamm. This is having higher reliability and fasteroperational speed but at a lower cost. It had a pre-fetch queue of 6-instructions and it issuitable for high volume applications such as computer workstations, word-processor andpersonal computers. It is made up of 134,000 MOS transistors and could work at clockrates of 4 and 6 MHz. This is also comes under first generation of Microprocessors. Intel released another 16 bit microprocessor 80286 having 1, 34,000 transistorsin 1982. It was used as CPU in PC-ATs in 1982. It is the second generationmicroprocessor, more advanced to 80186 processor. It could run at clock speeds of 6 to12.5 MHz .It has a 16-bit data bus and 24-bit address bus, so that it can address up to16MB of address space and 1GB of virtual memory. It had a pre-fetch queue of 6instructions .Intel introduced the concept of protected mode and virtual mode to ensure
proper operation. It also had on-chip memory management unit (MMU) .This waspopularly called as Intel 286 in those days. In 1985, Intel released the first 32 bit processor 80386, with 275,000transistors. It has 32-bit data bus and 32-bit address bus so that it can address up to a totalof 4GB memory also a virtual memory space of 64TB.It could process five millioninstructions per second and could work with all popular operating systems includingWindows. It has a pre-fetch queue of length 16-bytes with extensive memorymanagement capabilities. It is incorporated with a concept called paging in addition tosegmentation technique. It uses a math co-processor called 80387. Intel introduced 80486 microprocessor in the year 1989, with a built-in mathsco-processor and with 1.2 million transistors. It could run at the clock speed of 50 MHzThis is also a 32 bit processor but it is twice as fast as 80386.The additional features in486 processor are the built-in Cache of 8kB and built-in math co-processors. The addressbus here is bidirectional because of presence of cache memory. On 19th October, 1992, Intel released the Pentium-I Processor with 3.1million transistors. So, the Pentium began as fifth generation of the Intel x86architecture. This Pentium was a backward compatible while offering new features. Therevolutionary technology followed is that the CPU is able to execute two instruction atthe same time. This is known as super scalar technology. The Pentium uses a 32-bitexpansion bus, however the data bus is 64 bits. The 7.5 million transistors based chip, Intel Pentium II processor was releasedin 1997. It works at a clock speed of 300M.Hz. Pentium II uses the Dynamic ExecutionTechnology which consists of three different facilities namely, Multiple branchprediction, Data flow analysis, and Speculative execution unit. Another important featureis a thermal sensor located on the mother board can monitor the die temperature of theprocessor. For thermal management applications.
Intel Celeron Processors were introduced in the year 1999. Pentium-III processor with9.5 million transistors was introduced in 1999. It also uses dynamic execution micro-architecture, a unique combination of multiple branch prediction, dataflow analysis andspeculative execution. The Pentium III has improved MMX and processor serial numberfeature. The improved MMX enables advanced imaging, 3D streaming audio and video,and speech recognition for enhanced Internet facility.Pentium-IV with 42 million transistors and 1.5 GHz clock speed was released by Intel inNovember 2000. The Pentium 4 processor has a system bus with 3.2 G-bytes per secondof bandwidth. This high bandwidth is a key reason for applications that stream data frommemory. This bandwidth is achieved with 64 –bit wide bus capable of transferring data ata rate of 400 MHz. The Pentium 4 processor enables real-time MPEG2 video encodingand near real-time MPEG4 encoding, allowing efficient video editing and videoconferencing. Intel with partner Hewlett-Packard developed the next generation 64-bit processorarchitecture called IA-64 .This first implementation was named Itanium. Itaniumprocessor which is the first in a family of 64 bit products was introduced in the year2001.The Itanium processor was specially designed to provide a very high level ofparallel processing ,to enable high performance without requiring very high clockfrequencies .Key strengths of the Itanium architecture include ,up to 6instructions/cycle. The Itanium processor can handle up to 6 simultaneous 64 –bitinstructions per clock cycle. The Itanium II is an IA-64 microprocessor developed jointly by Hewlett-Packard(HP) and Intel and released on July 8,2002..It is theoretically capable of performingnearly 8 times more work per clock cycle than other CISC and RISC architectures due toits parallel computing micro-architecture. The recent Itanium processor features a split L2cache, adding a dedicated 1MB L2 cache for instructions and thereby effectively growingthe original 256KBL2 cache, which becomes a dedicated data cache. The first Itanium 2
processor (code named McKinley) was more powerful than the original Itaniumprocessor, with approximately two times performance. Pentium 4EE was released by Intel in the year 2003 and Pentium 4E was releasedin the year 2004. The Pentium Dual-Core brand was used for mainstream X86-architecturemicroprocessors from Intel from 2006 to 2009 The 64 bit Intel Core2 was released onJuly 27, 2006. In terms of features, price and performance at a given clock frequency,Pentium Dual-Core processors were positioned above Celeron but below Core and Core 2microprocessors in Intels product range. The Pentium Dual-Core was also a very popularchoice for over clocking, as it can deliver optimal performance (when over clocked) at alow price. The Pentium Dual Core, which consists of 167 million transistors wasreleased on January 21, 2007. Intel Core Duo consists of two cores on one die, a 2 MBL2 cache shared by both cores, and an arbiter bus that controls both L2 cache and FSBaccess. Core 2 Quad processors are multi-chip modules consisting of two dies similar tothose used in Core 2 Duo, forming a quad-core processor. While this allows twice theperformance to a dual- core processors at the same clock frequency in ideal conditions,this is highly workload specific and requires applications to take advantage of the extracores. In September.2009, new Core i7 models based on the Lynnfield desktop quad-core processor and the Clarksfield quad-core mobile were added, and models based onthe Arrandale dual-core mobile processor have been announced. The first six-coreprocessor in the Core lineup is the Gulftown, which was launched on March 16, 2010.Both the regular Core i7 and the Extreme Edition are advertised as five stars in the IntelProcessor Rating.TYPES : Today there are various types of microprocessors available in the market.Theyare classified in to different groups based on the bit length that the ALU can process inone clock cycle. Foe example, a microprocessor with a 4-bit ALU is referred to as a 4-bit microprocessor, regardless of the number of address lines or the number of data linesthat it has. Similarly 8-bit, 16 bit, 32bit and 64 etc. Based on the performance also
microprocessors are classified. They are , dedicated and embedded controllers, bit-sliceprocessors and general purpose CPUs etc..TECHNOLOGIES USED: The early microprocessors like 4004 were fabricated usingPMOS technology. Later INTEL used N-MOS technology and H-MOS technology tofabricate 8085 and 8086 microprocessors. Soon this was changed to CMOS technologywhich was a very popular fabrication technology used for all the advancedmicroprocessors.Later on this technology is replaced by BiCMOS technology which hasthe properties of both bipolar and CMOS technologies.Even today most of the processorsare fabricated using this technology. But recently there is advanced BiCMOS technology(ABT) under discussion and may emerge as a promising technology in the processorindustry.OVERVIEW OF 8086 MICROPROCESSOR FAMILY: In the 8086 microprocessorfamily we consider all the advanced microprocessors like INTEL 8088, 80186, 80286,80386 ,80486 processors.The Intel 8086 is a 16-bit processor that works as a CPU in a microcomputer. The term16-bit means that it’s ALU, its internal registers, and most of its instructions are designedto work with 16-bit binary words. The 8086 has 16-bit data bus, so it can read data fromor write data to memory and ports either16 bits or 8 bits at a time. The 8086 has a 20-bitaddress bus, so it can address any one of 220 = 1,048,576, memory locations. Sixteen bitwords will be stored in two consecutive memory locations. If the first byte of the word isat an even address, the 8086 can read the entire word in one operation. If the first byte ofthe word is at an odd address, the 8086 will read the first byte with one bus operation andthe second byte with another bus operation . The Intel 8088 has the same ALU, the same registers, and the same instructionset as that of 8086 processor. The 8088 has also a 20 bit address bus, so that it canaddress any one of 1,048,576 bytes in memory. But 8088 processor has only 8 bit databus so it can only read data from or write data to memory and ports, of 8 bits at a time.The Intel 8088 was used as the CPU in the original IBM personal computers(PC/XT). The Intel 80186 is an improved version of the 8086 and 80188 is the improvedversion of 8088. In addition to the 16 bit CPU 80186 and 80188 have programmable
peripheral devices integrated in the same package. The instruction set of 80186/80188 isa super set of the instruction set of 8086.I.e a program written for 8086/8088 willcertainly excute on 80186 or 80188 microprocessors but the converse is not true. The Intel 80286 is a 16 bit ,advanced version of the 8086 which is specificallydesigned for use as a CPU in a multi-user or multitasking microcomputer. Whenoperating in its real address mode 80286 works mostly as a fast 8086. Most programswritten for 8086 can run on an 80286 operating in its real address mode. The 80286processor was used in IBM PC/AT computers as the CPU. The Intel 80386 is the first 32 bit microprocessor which is upward compatiblefrom the 8086 ,80186 and 80286.It can directly address up to 4 gigabytes of memory.This 80386 contains more sophisticated features than 80286 processor which makes it towork in multi-user and multitasking applications. The architecture of 80386 is known asIA-32 architecture. This architecture extended all the address and general purposeregisters to 32 bits, which gave the processor the capability to handle 32 bit address, with32 bit data. The Intel 80486 is also a 32-bit microprocessor .This is the next member of theIA-32 architecture. This processor has the floating point processor integrated into CPUitself. The 80486 processor consists of an 8kB code and data cache memory. It has a fivestage instruction pipeline scheme which allows this to execute instructions much fasterthan 80386.The 80486 has 6 additional instructions when compared t0 80386 processor.ARCHITECTURE OF INTEL8086/8088: