Reviewing A Microprocessor Based System Design Information Technology Essay

Microprocessor is an electronic device which incorporates the functions of a processing unit in a single chip. It is a device which needs external peripherals to run. Unlike a microcontroller, it needs external interfacing of the peripherals like memory, counters etc. Though the term “microprocessor” has traditionally referred to a single- or multi-chip CPU or system-on-a-chip (SoC), several types of specialized processing devices have followed from the technology. The most common examples are microcontrollers, digital signal processors (DSP) and graphics processing units (GPU).

Given above is the picture of intel 8085 microprocessor. The Intel 8085 is an 8-bit microprocessor introduced by Intel in 1977. The “5” in the model number came from the fact that the 8085 required only a +5-volt power supply.

8085 microprocessor is an 8-bit microprocessor with a 40 pin dual in line package. The address and data bus are multiplexed in this processor which helps in providing more control signals. 8085 microprocessor has 1 Non-maskable interrupt and 3 maskable interrupts. It provides serial interfacing with serial input data (SID) and serial output data (SOD).

This is a separate unit which can perform operations to perform arithmetic operations like +, -, *, / and logical operations like AND, OR, NOT etc. These operations are performed by the Arithmetic and Logic Unit (ALU). ALU performs these operations on 8-bit data.

General Purpose Registers

Apart from accumulator 8085 consists of six special types of registers called General Purpose Registers. These general purpose registers are used to hold data like any other registers. The general purpose registers in 8085 processors are B, C, D, E, H and L. Each register can hold 8-bit data. Apart from the above function these registers can also be used to work in pairs to hold 16-bit data. They can work in pairs such as B-C, D-E and H-L to store 16-bit data. The H-L pair works as a memory pointer.

Program Counter and Stack Pointer

Program counter is a special purpose register. A program counter stores the address of the next instruction to be executed. In other words the program counter keeps track of the memory address of the instructions that are being executed by the microprocessor and the memory address of the next instruction that is going to be executed.

Temporary Register:

As the name suggests this register acts as a temporary memory during the arithmetic and logical operations. Unlike other registers, this temporary register can only be accessed by the microprocessor and it is completely inaccessible to programmers. Temporary register is an 8-bit register.

Microprocessor Based Systems:

Microprocessor based systems, also known as MBS, are those systems in which the key component is a microprocessor. This microprocessor is interfaced with one or more external components, and it is necessary that this system must provide the desired result.

This figure above shows a block diagram of a MBS in general sense. It consists of the following component parts:

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Central processing unit ( CPU)

Memory chips: various types of RAM and ROM

Address decoder chip

Processing devices

Bus structure

CPU-The CPU is usually a single VLSI (very large-scale integration) or ULSI (ultra large scale integration) chip containing all the necessary circuitry to interpret and execute program instructions such as data manipulation, logic and arithmetic operations and timing and control. The capacity or size of a microprocessor chip is determined by the number of the data bits it can handle. A16-bit chip has a 16-bit data width; a 32-bit processor has a 32-bit data width and so on.

Memory: 2 types of memories are found: ROM and the RAM.

RAM allows the writing and the reading. It requires being refreshed regularly. Indeed, the data (1 or 0) are safeguarded by capacitive effect in a transistor. The RAM are connected by outside by the address bus and the data bus.

A ROM memory is reading only and directly programmed by the manufacture of the electronic circuit. The contents (program – data) are thus not modifiable.

So of other circuits of the ROM type modifiable are used: Eprom (Electric PROM) programmable in 1 time EEprom (Electric Erasable PROM), which one can erase completely several times and Rom Flash that one can write directly by an electric signal. All these circuits keep information if the supply voltage is cut.

Bus Structure:

The interfacing of the processor towards the control circuit requires 3 bus system: a data bus, an address bus and a control bus. A bus is a whole of lines of communication which connects 2 or more digital circuits between-them.

Each site report or peripheral internal is indicated by address specific similar with the postal address. A specific address cannot be divided between several circuits. The address bus makes it possible the processor to communicate with the peripheral via its address. An address bus consists of several lines. An address bus 8 bit corresponds to 8 lines of addresses and can thus address 28 different addresses, that is to say 256 different addresses, and so on. The higher the number of line of address is, the more the processor is able to manage peripherals.

Once the peripheral contacted via the address bus, the data bus makes it possible to transfer from the binary data in reading or in writing. The data bus consists of a certain number of lines. All the capacities of the data buses are indicated under 8 lines of data (in Byte – byte), or in multiple of 8 bits, the current processors use 64 lines of data for example. Thus 1 MB of memory means 1 MB under 8 lines, i.e. 8 Mb.

A Control bus synchronizes the transfers of data between the processor and the peripherals (memory, inputs/outputs). It ensures the dialogue necessary for the transfer of the data or the address indicated. The signals of the bus of order also make it possible to manage the interruptions, orders specific which make it possible an external circuit to announce to the processor which it is ready to receive from the data of outside for example. Low signal means that it is active when the signal is to 0 V, not credit when the signal is in a high state (5V). The sequences present on the bus of order are also specific to the processors.

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Practical Examples of Microprocessor Based Systems:

Motherboards of Computers

We are surrounded by countless MB systems in the present world. The biggest examples that we see today of an MBS is the motherboard of our personal computers. A motherboard is the central printed circuit board in many modern computers and holds many of the crucial components of the system, while providing connectors for other peripherals.

A typical personal computer has its microprocessor, main memory (RAM), and other essential components connected to the motherboard. Other components such as external storage, controllers for video display and sound, and peripheral devices may be attached to the motherboard as plug-in cards or via cables, although in modern computers it is increasingly common to integrate some of these peripherals into the motherboard itself.

Given below is the picture of the motherboard of a typical personal computer. Here we can see the different peripherals. A motherboard is the complete setup of a microprocessor based system. It has interfacings with the memory, the graphics cards, the external devices like power supply, the heat sinks, the Disk drives, the external peripheral slots.

A motherboard has a minimum of the following components:

Microprocessors. These are usually Intel’s processors used in today’s life.

Main memory chips. It is usually DDR RAM memory now a days.

a chipset which forms an interface between the CPU’s front-side bus, main memory, and peripheral buses

BIOS firmware memory chips.

a clock generator which produces the system clock signal to synchronize the various components

external slots for various components like Graphics cards, memory extension, modems

power connectors, which receive electrical power from the computer power supply and distribute it to the CPU, chipset, main memory, and expansion cards.

Microprocessor Based Security Systems (Access Control Systems):

Access Control System is used in the places where we need more security. It can also be used to secure lockers and other protective doors. The system comprises a number keypad and the keypads are connected to the 8 bit microprocessor 8085 through the programmable peripheral IC 8255. The microprocessor continuously monitor the keypad and if somebody enters the password it will check the entered password with the password which was stored in the memory and if it they are same then the microprocessor will switch on the device. The password can be a four digit number. If we enter the correct password then the microprocessor will switch on the load. Otherwise, it will not respond. A typical example of the simple circuit and data flow of a MB Access control system:

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Microprocessor Based Fire Monitor Alarms:

Fire Monitoring system is used to monitor the Temperature of two Rooms and if the sensor found any fire in the Room then the alarm will be switched ON until the Fire is put off else the Reset button is pressed. The Fire is sensed by using the Thermistor. The Thermistor is a passive device which has a Negative Temperature Co-efficient (NTC), i.e when the temperature increases then the resistance of the Thermistor will decrease. A analog comparator is used for the fire sensor circuit , at normal temperature the output of the comparator is low, and if there is any fire hazard, then the temperature increases and therefore the resistance of the Thermistor decreases and the output of the comparator goes High which Trigger the Microprocessor though the PPI 8255. Then the Microprocessor will switch ON the Alarm for fire. The above system is monitored and controlled by the 8 bit Microprocessor. The Microprocessor continuously monitors the two sensors and if any one of the sensor sense Fire then it latches the sensor and the microprocessor switch on the Alarm according to the software stored on the RAM.

Advantages of MBS’s

These systems are totally user programmable.

They can be customised according to the will of the user.

High speed

Great efficiency

Highly accurate

Very small size

Have a wide range of applications.

Can be interfaced with countless peripherals.

Logical decisions are easily obtainable

They work with not only digital, but also with analog systems.

They are the base of highly complex computing systems.

Have completely revolutionised the way the electronic equipment work.

Have given an advanced approach to various applications like security systems.

Are in rapid development phase. As such, they are responsible for the development of electronic systems.


They do not work on high voltages. As such, sometimes a relay network may be needed.

They work mostly on DC voltages.

Efficiency is affected by external changes like temperature.

Complex circuits are sometimes very tough to troubleshoot.


It is thus clear that the microprocessor based systems are one of those most important constituents of electronics. These systems have completely revolutionized each and every sphere of the electronic systems. Our most of the gadgets that we use are based on microprocessor systems. Personal Computers, Smartphones, Digital Cameras, Netbooks, IPods and what not…. Countless systems form a base with these microprocessor based systems. No electronic gadget is possible without the microprocessor based systems. They form the base to the microcontroller systems which are a really advanced version of a single chip microprocessor based system. Thus, we can conclude that Microprocessor based systems are one of the most important aspects of electronic instrumentation science.

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