Digital Electronics

Microprocessor Intel 80 x 86 and Motorola 680 x 0 Family

Microprocessors Introduction

A digital integrated circuit device which can be programmed for performing arithmetic, logical and other operations and which process data in a specific manner, is called microprocessor. In other words, microprocessor is a type of digital integrated circuit device which is programmed under a series of instructions for performing data specific functions. Micro means a component with a small physical size while processor is that part of some system which performs basic functions according to received instructions and process data in accordance with the stored program on it. As such, microprocessor is a silicon chip- made small device which conducts arithmetic, logical and other basic operations. Remember that, when a microprocessor is connected with a memory device and data is transmitted on it from outside or data is transferred outside from it, such a microprocessor becomes a micro-computer.

A microprocessor basically consists of following three elements, as has been illustrated by figure 11.1 and 11.2;

1). Arithmetic Logic Unit

2). Register Unit or Memory Device

3). Control Unit

Arithmetic logic unit (as its name suggests) performs arithmetic operations e.g. addition, subtraction, multiplication, division etc. and logical operations e.g. NOT, AND, OR and XOR etc.

A register unit consists of multiple registers, where in data is temporarily being stored for implementing a program or a series of instructions on a register. That’s this unit stores data and information (useful information obtained after the data process operation is called information) so that the same could be used again as and when required. Memory unit which consists both of RAM and ROM, has been connected with microprocessor by means of address and data buses and read and write control, as illustrated by figure 11.3


Figure 11.1 – the basic elements of a microprocessor


Figure 11.2 – sections of a digital computer


A control unit provides timing and control signals for entering data into microprocessor or receiving data from the microprocessor, so that microprocessor could operate in accordance with the programmed instructions and all other factors. In other words, besides supervision of an entire digital system, control units also control it. This unit transmits data on desired devices for operation and also controls flow of data. The control signals of a microprocessor have been illustrated vide figure 11.4.

Figure 11.4 – Control signals in a microprocessor


Remember that if arithmetic logic unit (AMU), memory unit (MU) and control unit (CU) are combined together in a place or device, such a device is called central processing unit (CPU), which is a brain and central unit of every computer and controls operation of any computer. A CPU fetches coded instructions from memory in a binary form, decodes it on a series of simple operations and follows a sequence of steps in order to fulfill these actions. Thus, a microprocessor always works on the principle of fetch, decode and execute sequence (i.e. fetch – decode – execute sequence).

The collection of 3 blocks illustrated in the center of figure 11.2 is often known as CPU. These three blocks (arithmetic section, memory section and control section) normally exist on a single circuit board. Whereas all devices outside a CPU are generally known as peripheral devices.

In short, a microprocessor (as its name implies) is a micro digital device in the type of an IC chip, which undertakes the function of processing data or other set of instructions and this is the reason, it is called a processor (however, it should be inculcated that set of instructions provided on a computer is known as data or facts prior to its processing by means of a processor. The process, which processing unit of a computer performs immediately after fetching data in order to make it more meaningful, is called processing. And further useful information, which are received after the process of data processing, is called information or output data). As such, microprocessor is such a central processing unit (CPU) which is fabricated on a single silicon chip, whereas CPU is such an electronic circuit which translates data or instructions, acts accordingly and implements it and controls input and output.

In order to transfer data or information internally and externally into a micro- processor, following three types of buses are uses, as has been illustrated by figure 11.5.

1). Address Bus

2). Data Bus

3). Control Bus

Address bus is just similar to a one – way street. By means of which microprocessor transmits address code on memory any other external device. The width or size of address bus depends on that particular number of bits, which it can controls or handle. Previously, microprocessors used to consist of 4-bit address buses. However, now with the development of microprocessor technology, their number has increased to 8, 16, 20, 24 and 32 bits. The more the number of bits on an address bus, the higher the number of memory locations for which microprocessor functions or up to the point, till which microprocessor can access memory locations. Similarly, if the number of bits is 16 and 32, 65,536 and 4,295,000,000 memory locations can be accessed respectively.

Figure 11.5 – Microprocessor buses


In other words, an address bus consists of 8, 16, 20, 24 or 32 signal parallel lines by means of which a CPU transmits memory address on this memory location, which is desired to be read or where something is desired to be written. The number of memory locations, which a CPU can address, is determined through the number of address lines. If N address lines exist on a CPU, it can directly address 2N memories. For example, a 16 address lines CPU, can address a total of 216 or 65,536 memory locations.

Data Bus is a two- way street, by means of which data or instruction codes are entered or transferred to microprocessor or through which some operation or arithmetic conclusion is transferred out from microprocessor. A data bus can handle 8 bits, 16 bits, 32 bits or 64 bits, however this depends on microprocessor. In other words, a data bus consists of 8, 16, 32 or 64 parallel signal lines and data bus lines are bidirectional. It means that a CPU can read data being transmitted into memory by means of these lines and can also transfer data out from memory through via lines.

Control Bus is used in order to coordinate or control different operations of a microprocessor with external devices, so that its operations could be understood with the help of these external devices. Control Bus consists of 4 – 10 parallel signal lines.

As a founder, Intel Corporation has played an extremely important role for development and marketing of microprocessors and this is the reason mostly Intel processors are used even today in most of the computers in the world. Some of the famous microprocessor numbers of Intel Corporation 8085, 8080, 8088, 8086 and Pentium series are particularly worth mentioning. Intel manufactured its first 4 – bit data bus 4004 micro – processor in 1971. Another 8 – bit 8008 number processor was immediately manufactured after this device. During mid-1976, two more 8- bit microprocessors number 8080 and 8085 were introduced. Both these devices could address 216 or a total of 65,536 memory locations due to having 16 – bit address Buses (i.e. their memory capacity was 64 kilo bytes).

Microprocessor’s Intel 80 x 86 Family

In 1978, Intel introduced 80×86 microprocessors family which initially consisted of 8086, 8088 and 80186 number processors, sometimes after which 80286, 80386 and then 80486 number processors entered the market. However, Pentium series is fifth generation of Intel microprocessors which is most popular and an advanced form as compared to all previous types.  Remember that every new generation of micro – processors is manufactured on the basis of basic facts of previous generation with the exception that some additional features related to a high speed and better performance are included in every new generation micro – processors. A brief detail of 80 x 86 microprocessor series is as follows;

8088, 8086 and 80186

In 1978, first processor of 80 x 86 family was manufactured, on the basis of which all subsequent processors were later on constructed. 8086 was a 16-bit (or 16-bit data base) micro – processor. The number of its address lines had been increased to 20, therefore it had a capacity to address 220 or 1,084,576 (i.e. 1 megabytes) memory locations. Different versions of 8086 series could be operated on 5MHZ, 8MHZ or 10MHZ clock frequencies.

8088 is basically similar to a 8086 micro – processor, which was manufactured one year later in 1979. It is also a 16 – bit micro – processor. The number of registers within it is relatively large and it provides comparatively large addressable memory space. It is being profusely used in IBM personal computers (PC).

80186 micro – processor is also basically similar to a 8086 micro – processor, except that some additional features like clock generator, system controller, interrupt controller and direct memory access (DMA) controller exist on one chip. Further, as a result of increase in its clock frequency up to 12.5MHZ, clock frequency ratio in 5MHZ 8088/ 8086 drop. As a result, facility to select any one of 8MHZ, 10MHZ and 12.5MHZ clock frequency also been generated.


In 1982, 80286 micro – processors were introduced. Its addressing lines capacity was enhanced up to 24 address lines, owing to which it can provide address on 224 or 16,777,216 memory locations (16megabytes). An advance mode – off operation, which is known as protected mode, was first used in 80286. As a result of this mode, some extra features like access to additional memory locations and advance programming were attained. However, remember that both 80286 and 80186 operate on same clock frequency.


In 1985, Intel Corporation introduced first 32 – bit 80386 micro – processor. 80386 micro – processor comprises 32-bit data bus and 32-bit address.

With 32 address bits, it can access up to 232 = 4, 294, 967, 296 memory locations (4 gigabytes). Apart from some extra added features, 80386 was first Intel micro – processor, the operational speed of which was relatively high. Different versions of 80386 operated on different clock frequencies, out of which 16MHZ, 20MHZ, 25MHZ and 33MHZ frequency types are commonly available. Amongst other economical versions of 80386, 80386SX and 80386SL are also worth mentioning, where in data bus can be reduced up to 16 – bits and address bus up to 24 bits.


In 1989, 8 kilo byte cache memory chip was discovered, as a result of which memory access times declined further as a result of setting it between processor and main memory. Thus, a new stage was added to the evolutionary stages of a micro – processor, owing to which fast – paced SRAM were being started to use instead of relatively slow – paced main memory (DRAM). Different versions of 80486 can generally operate up to 66MHZ clock frequencies.


In 1993, Pentium processor was invented, which consists of 32 address bits similar to 80486. However, number of data bits in it is twice as the number of data bits in 80486 (i.e. 64 bits). In Pentium, 2 cached memories of 8 kilo bytes also exist, one of which is reserved for instructions and other for data. in the present era, Pentium is also available in a series (e.g. 1,2,3,4 etc.), where in the existing Pentium processors can operate from 166MHZ to more than 800MHZ clock frequencies.

Motorola Microprocessor 680 x 0 Family

Motorola is the second largest company after Intel Corporation, which has gained tremendous achievements in the field of microprocessors. The 6800 series micro – processors of the company, on the basis of which Apple computers were manufactured, are extremely popular. The first Motorola micro – processors were 8 – bit devices, which consisted of 8 – bit data bus. The 6800 series micro – processors were introduced in 1975, which had a clock frequency of 2MHZ and which had a capacity to address 64 bytes memory with a 16 – bit address bus. After this, 6802 processor was manufactured, where in a 128 kilo bytes RAM was used in place of few registers. Clock frequency in 6803 was enhanced up to 3.58 MHZ in 6803 and an UART (Universal Asynchronous Receiver / Transmitter) was inducted in this micro – processor for serial communication. The final 8 – bit micro – processor was 6809in which apart from multiply instruction other instructions were added. All these 8 – bit devices consisted of a maximum of 16-bit address bus.

In 1978, 16 – bits processors of Motorola corporation were introduced as 68000. They had 24 address lines and had a capacity to access 16 megabytes memory, though Intel’s 8088 and 8086 micro- processors could access just one megabyte of memory at that time. Therefore, owing to higher clock frequency (16MHZ) Motorola ‘s 68000 series processors were extremely fast as compared to Intel devices of the time. As a result of further advancement in these 68000 series, 68020, 68030, 68040 and 68060 micro – processors were manufactured. Micro – processors manufactured in 68020 series, contained 32 – bits and they had a capability to address 16 gigabytes of memory. It also comprised a 25 bytes cache memory for instructions, which was considered a great feature of the time. Moreover, the clock frequency of these processors was also increased up to 33MHZ. In 668030 devices, another cache memory of 256 byte was inducted and its operational speed was also enhanced up to 50MHZ. In 68040 devices, an addition of 4 kilo bytes was done in data and instruction cache memory and a math compressor was also included on to its chip. The range of cache memories was increased to 8-Kbytes on 68060 device and its processor’s speed or clock frequency was also increased to 66MHZ.

Motorola’s power PC or MPC 601 are such type of micro -processor, which comprise 64 – bits and can effectively accomplish three instructions simultaneously on one clock pulse. Every one of its cache memories is of 32 kilo bytes each and an internal math processor also exists on it. It is a special type of chip which handles complex arithmetic questions, which a traditional micro-processor cannot solve in a better manner. Power PC is a RISC type microprocessor (RISC means Reduced Instruction Set Computing) i.e. bringing improvement in its performance by means of reducing number of instructions. The clock frequency of such processors is up to 350MHZ. These processors have further been developed during the recent times.

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My name is Shahzada Fahad and I am an Electrical Engineer. I have been doing Job in UAE as a site engineer in an Electrical Construction Company. Currently, I am running my own YouTube channel "Electronic Clinic", and managing this Website. My Hobbies are * Watching Movies * Music * Martial Arts * Photography * Travelling * Make Sketches and so on...

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