Introduction to Microprocessors and Organization of 8085

Scope of the Syllabus for Introduction to Microprocessors and Organization of 8085

Probable marks : 21

Above probable marks means : In board exam questions asked form this chapter are nearly for 21 marks out of 50 Marks.

Scope of the Syllabus

1. Evolution of microprocessors.

2. What is microprocessor ?

3. Block diagram of generic microprocessor and study of various blocks in it.

4. Block diagram of 8085 microprocessor.

5. Study of various blocks and functions of various pins in 8085 microprocessor.

Q.1 What is microprocessor ? List its functions.

Ans :

1) Microprocessor is a semiconductor, multipurpose, programmable logic device that reads binary instructions from a storage device called memory, accepts binary data as input and according to the instructions and provides result as output.

2) The electronic logic circuits in microprocessor are capable of performing various computing functions and making decisions to change the sequence of program execution.

3) Microprocessor can also be viewed as an integrated circuit, that contains processing capabilities of large computers.

4) A microprocessor can be roughly divided into three parts :

microprocessor can be roughly divided into three parts

A.L.U is arithmetic and logic unit, where arithmetical and logical operations are carried out. Registers are primarily used to store data temporarily during execution of program.

Control unit provides timing and control signals to the whole system. It also controls flow of data.

5) The functions of microprocessor are given below :

a) To fetch, decode and execute instructions.

b) To transfer data from one block to another block or from one block to I/O lines.

c) To give proper response to different externally produced interrupts according to their, priority.

d) To provide control and timing signals to the whole system according to the instructions

Q.2 Write a short note on evolution of microprocessor giving one example of each generation.

  Asked in Board Exam  (March 2002, 2003, 2004, 2005, 2008; Oct. 2003, 2004, 2007,09 )  Important

Ans :

The evolution of microprocessor can be explained by following five generations :

(i) First generation :

(a) Intel’s 4004 was the first microprocessor available in the market. It was a four bit microprocessor introduced in 1971, designed to be used in calculators.

(b) In 1972, Intel introduced first general purpose 8-bit microprocessor Intel 8008.

(c) It was followed by Intel’s 8080 in 1973 and Motorola’s 6800 in the same year.

e.g. Intel’s 4004 (4-bit), 8008 (8-bit)
Motorola’s 6800 (8-bit)

(ii) Second generation :

(a) In 1974, Intel’s 8080, Zilog’s Z-80, Motorola’s M6800 were introduced. All these were 8-bit

(b) During second generation, the development of microprocessor has been in a direction to complete microprocessor system (microcontroller) ie. CPU, ROM, RAM, clock, I/O ports all in single package.

(c) In 1976, INTEL’s 8085, 8-bit microprocessor was introduced.

(d) In 1977, 12-bit microprocessor Intersil’s IM6100 and Toshiba’s T8190 developed.

eg. INTEL’s 8085 (8-bit)
Zilog’s Z80 (8-bit)

(iii) Third generation :

(a) Intel introduced first 16-bit microprocessor 8086 in 1978.

(b) It was followed by Zilog’s Z-8000 in 1979 and Motorala’s 68000 in 1980.

(c) In third generation, memory space was 64 KB. The other features were full arithmetic execution and efficient higher level language addressing.

e.g. Intel’s 8086 (16-bit), Zilog’s Z-8000 (16-bit)

(iv) Fourth generation :

(a) In 1981, Intel introduced first 32-bit microprocessor 80386. It can address physical memory of 4 GB.

(b) Other 32-bit microprocessor Hewlett Packard’s HP-32 announced in 1982.

(c) In 1987, Motorola’s 68020, a 32-bit microprocessor introduced.

e.g. INTEL 80386 (32-bit)
INTEL 80486 (32-bit)

v) Fifth generation :

(a) Intel made improvement in microprocessor design to provide the greatest speed.

(b) Also system can run on new OS like UNIX, LINUX etc.

(c) The processor in this generation is called Pentium. It is 64-bit microprocessor

e.g Intel 80586, Intel Pentium IV.

Q.3 Draw a neat block diagram of microcomputer system ? Explain each block function in brief.

  Asked in Board Exam  (Mar. 1998, 2003, Oct. 2008)  Important

Ans : Block Diagram of Microcomputer :

Draw a neat block diagram of microcomputer system

Microcomputer mainly contains following blocks :
1) Input device (keyboard)

2) Microprocessor Unit (MPU)

3) Program memory (ROM)

4) Data memory (RAM)

5) Output device (7-segment display)

Fig.1.1 shows detail architecture of a microcomputer with all essential bus and signa lines.

1) Input Device (Keyboard) :

The instructions as well as data prepared for particular program are entered through input device like keyboard.

2) Keyboard Interface :

Due to following reasons it is necessary to connect keyboard to keyboard interface.

i) When instruction and data is entered through keyboard, it is not possible to feed the instruction directly to MPU because MPU may be busy in performing previous instruction or other task.

So it is stored in a special chip called keyboard interface.

ii) The speed of input device and MPU may not be equal.

3) Microprocessor Unit (MPU) :

i) MPU processed system data and required control signals are generated to control the system.

ii) All processing and data flow is done in the system with MPU chip.

4) ROM (Read Only Memory) :

i) It contains permanently stored program known as monitor program.

ii) It has address bus, chip select and read signal line.

iii) lt allows only to read stored information.

5) RAM (Random Access Memory) :

i) It is used to store data, it is a temporary storage device.

ii) Reading and writing of data into memory, so bidirectional data bus is required.

6) Output Device (7 Segment Display) :

Output of the system | ie. stored data in display interface are displayed on seven segment display.

7) Display Interface :

A special display interface circuit or IC is used to store data and drive the display.

8) Address Decoder :

It decodes the address and selects the proper chip (device).

9) Clock:

i) Whole circuitry is synchronized with clock.

ii) The speed of the system depends on the clock frequency.

10) Power Supply :

Power supply is necessary to operate the circuit.

Fig.1.1 also shows following important lines :

  Asked in Board Exam  (Oct. 2007)  Important

1) Interrupt line : used to interrupt the MPU.

2) Address bus : 16-bit address bus (unidirectional) from the MPU used to flow bits of required memory to devices.

3) Data bus : 8-bit bidirectional data bus used to transfer data among MPU and devices.

4) Control bus : It carries control signals generated by MPU.

5) Power line : It is necessary to operate the circuit.

Q. 4 List any three primary functions of CPU of microcomputer.

  Asked in Board Exam  (March 2002, 2004, 2006, 2008. Oct. 2003, 2005)  Important

Ans : The primary functions of the CPU of a microcomputer are –

1) To fetch, decode and execute program instructions in the proper order.

2) Transfer data to and from memory and to and from the input/output sections.

3) Responds to external interrupts.

4) Provide overall timing and control signals for the entire system.

Q.5 Draw a labelled block diagram of generic microprocessor. Explain its functional units.

  Asked in Board Exam  (March 2005; Oct. 2003, 2006, 2007)  Important


Q.5 Draw a neat simplified block diagram of CPU architecture of micro-computer.

  Asked in Board Exam  (March – 2009, Oct -2010)  Important

Ans: Block Diagram of Generic Microprocessor :

generic microprocessor | Draw a neat simplified block diagram of CPU architecture of micro-computer

Microprocessor is a primary functioning unit.

Fig.1.2. shows the detailed block diagram of generic microprocessor. i.e general microproccess It consists of following blocks:

i) Arithmetic and Logic unit.

ii) Several registers – Instruction register, Accumulator, Stack pointer, Status register,Temporary register, Data/Address register.

ii) Program counter.

iv) Instruction decoder.

v) Timing and control section.

vi) Bus buffer and Latches.

vii) Interrupt control.

1) Arithmetic and Logic Unit :

a) This unit performs arithmetic and logic operations.

b) This unit also performs rotate operation.

c) The operations in this unit affects the status register.

d) The results from ALU are placed in accumulator.

2) Several Registers :

i) Accumulator :

a) Accumulator is an 8-bit register used to store 8-bit data.

b) In arithmetic and logic operation, result is stored in accumulator.

ii) Instruction Register :

a) This is an 8-bit register.

b) The first byte of an instruction is stored in this register.

iii) Status Register :

a)Status register is called as flags, which consist of flip-flops that are set or reset according to data conditions in accumulator.

b) The generic MPU has two flags : Zero and carry flag.

iv) Program Counter :

a) It is a 16-bit register containing the address of next executable instruction.

b) It can be incremented or reset by the control section.

v) Stack Pointer :

a) It is al6-bit register consisting of address of memory location called stack.

b) Stack is R/W memory used for temporary storage.

vi) Data/Address register :

a) The data/address register is a two 8-bit registers that can be used separately or as a combined
pair. They are labelled as H and L.

b) Data is stored in these registers. When used in pair, 16 bit address can also be stored.

3) Instruction Decoder :

a) This interpretes the content of instruction register and determines exact steps to be followed
in executing the entire instruction.

b) It directs the control section accordingly.

4) Timing and Control Unit :

a) This section receives the signals from the instruction decoder to determine the nature of
instruction to be executed.

b) Timing and control signals are sent to all parts of microprocessor.

5) Address Bus:

a) The address bus is a group of 16 lines generally identified as A0 to A415.

b) It is a unidirectional bus i.e. bits flow in one direction from MPU to peripheral devices.

6) Data Bus:

a) Data bus is a group of 8-bits used to data flow.

b) It is a bidirectional bus i.e. data flows in both directions between MPU and memory and

7) Bus buffer and Latches :

a) Latch is a flip-flop used to store one bit of information.

b) Information is stored into latch by enabling buffer.

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