Microprocessor Intrpduction

7/29/2019 Microprocessor Intrpduction

1/16

BASICS OFMICROPROCESSOR[8MARKS]

Chapter1

Chapter Details1.1 Evolution of Microprocessor

1.2 Salient Features of 8085Microprocessor

1.3 Pin Diagram of 8085 andDescription

1.4 Architecture of Intel 8085

1.5 8085 System Bus

1.6 Demultiplexing of AD0-AD7 of 8085

1.7 Limitations of 8-bit Microprocessor


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1-2 Microprocessor & Programming

Graphical and Statistical representation of questions asked from this chapterin previous years MSBTE Question Papers

Statistical Analysis

MSBTE paper Total marks questions asked in this chapter

S-2010 08W-2010 08

S-2011 08


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Basics of Microprocessor 1-3

1.1 EVOLUTION OF MICROPROCESSOR

A common way of categorizing microprocessors is by the

number of bits that their ALU can work with at a time.

The first commercially available microprocessor was the Intel4004 produced in 1971 and known as 4-bit processor.

It contains 2300 PMOS transistors and mostly used with

calculator.

In 1972 8008 microprocessor is produced known as 8-bit

microprocessor but requires 20 or more additional devices to

form a functional CPU.

In 1974, Intel introduced the 8-bit microprocessor which has

much larger instruction set than 8008 and requires only twoadditional devices to form a functional CPU. After that Motorola

came out with MC6800 as 8-bit general purpose CPU. It has the

advantage that it requires only +5V power supply.

In 1977 Intel produced 8085 microprocessor. It was

implemented with 6200 transition on a single chip NMOS

device.

In 1978 to 1982 Intel introduced 16-bit microprocessors 8086microprocessor. 0186/80286 which are used for embedded

control applications. These processors were implemented withNMOS technology which was more faster than NMOS.

In 1985 to 1989 32-bit microprocessor 80386/80486 were produced. They can directly

access upto 4 GB of memory and had multiuser and multitasking features.

80486 added more parallel execution capability with 5 pipeline stages. It also has built in

math co-processor and 8 kB code and data cache.

Pentium produced in 1993 which has superscalar, super pipelined architecture.It has 2 pipelines where each one is a 4 stage pipeline.

Then Pentium Pro P-I, P-II, P-III and P-IV are developed. All are 64-bit microprocessor.It can directly address upto 64 GB memory.

P-II supports multimedia extension instruction.

P-III supports and has been developed by using 0.25 micro technology.

Microprocessor:It isan electronic devicemade up of silicon

technology which can

compute mathematicaland logical operations.

BTE[S.10,W.10]-2MDescribe evolution

of microprocessor

with suitableexamples.

OrGive evolution of

microprocessor.


4/16


1.2 SALIENT FEATURES OF 8085 MICROPROCESSOR

i. 8085 microprocessor can read or write or perform

arithmetic and logical operations on 8-bit data at time.

ii. It is a single chip NMOS device implemented with 6200transistors.

iii. It requires +5V power supply.

iv. It provides on chip clock generator.

v. Maximum clock frequency is 3 MHz and minimum clock frequency is 500 kHz.

vi. It provides 74 instructions with five addressing modes.

vii. It provides 5 hardware interrupt and 8 software interrupts.

viii. It has 8 data lines and 16 address lines hence capacity is 216 = 64 kB of memory.

ix. It can generate 8-bit I/O address so 28 = 256 input and 256 output ports can be

accessed.

x. It provides two serial I/O lines SID and SOD so that serial peripherals can be

interfaced directly with 8085 microprocessor.

1.3 PIN DESCRIPTION

X1X2

RESET OUT

SOD

S DI

TRAP

RST 7.5

RST 6.5

RST 5.5

INTR

AD0

INTA

AD1

AD2

AD3

AD4

AD5

AD6

V (GND)SS

AD7

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

18

17

19

20

39

40

38

37

36

35

34

33

32

31

30

29

28

27

26

25

24

23

22

21 A8

VCC

HOLD

HLDA

CLK OUT

RESET IN

READY

IO / M

S1

RD

WR

S0

ALE

A15

A14

A13

A12

A11

A10

A9

P

INTELIC

8085

Figure 1.1: Pin diagram of 8085

SID:Serial InputDevice

SOD:Serial Output

Device


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Pin Description

The microprocessor 8085 is a 40 pin INTEL IC whose internal circuit is made of 6200

transistors. The microprocessor 8085 consists of following pins.

1. X1, X2: A Quartz crystal is connected on pin X1, X2 whichis used to generate the system clock of the frequency

3.14 MHz.

2. RESETIN : This is an active low input reset signal used

to reset microprocessor. When the signal on this pin is

low, the program counter is set to zero. The buses are tri

stated and the microprocessor is reset.

3. RESETOUT: This is active high output signal generated by microprocessor after

receiving RESET signal and used to reset other devices in the system.

4. SOD, SID: The SOD stands for Serial Output Data and SID stands for Serial InputData. These two pins are used to perform serial communication with

microprocessor. The SID pin is used to receive data serially from external devices

and similarly the SOD pin is used to output data serially by microprocessor for

external devices.

5. Hardware Interrupt Pin: (TRAP, RST 7.5, RST 6.5, RST

5.5, INTR) microprocessor consists of five differenthardware interrupt pins which are TRAP, RST 7.5, RST

6.5, RST 5.5 and INTR.

The TRAP is the highest priority interrupt followed by RST 7.5, RST 6.5,

RST 5.5 and INTR which is the lowest priority interrupt.

Whenever the microprocessor is interrupted it will branch from the main programto a sub program called as ISR (Interrupt Service Routine).

X

Pbran

ches

Preturnsback

HLTRET

ISRP

(Main Program)M/P

AB

Interrupt

Figure 1.2: ISR

X1

Quartz crystal

X2

RST:Restart Interrupt

TRAP:Non MaskableInterrupt


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After executing the entire sub program or ISR microprocessor returns back from the

sub program to the main program by executing instruction RET (Return).

6. INTA (Interrupt Acknowledgement): If microprocessor is interrupted by INTR

signal then it will generate logic 0 on INTA pulse.

TheINTA is used to get the sub program address from external devices.

7. Address Lines (A15-A8 and AD7-AD0): The microprocessor 8085 has 16 bit address

lines from A15-A8 and AD7-AD0. These lines are used to transfer 16 bit address of

memory as well as 8-bit address of I/O ports.

The lower 8 lines (AD7-AD0) are often called as multiplexed data lines.

8. Status Pins (S1, S0): The microprocessor 8085 has two status pins as S1, S0 which is used to

indicate the status of microprocessor or operation which is performed by microprocessor.

S1 S0 Operation

0 0 HLT state

0 1 Writing operation1 0 Reading operation

0 1 Opcode fetch operation

9. ALE (Address Latch Enable): The ALE signal is used to enable or disable the

external latch IC (74373/8212).

The external latch IC is used for the demuiltiplexing of AD7-AD0 lines, i.e., it is

used to separate the address and data from AD7-AD0 lines.If ALE = 1/0 then external latch IC is enabled / disabled respectively.

10. RD : Read: This is active low signal which indicates that the selected I/O or

memory device is to be read and also is available on the data bus.

11. WR : Writing: This is active low signal which indicates that the data on data bus

are to be written into a selected memory location.

12. IO/ M : (Input / Output / Memory): This is used to select either Input / Output

devices or memory operation. When it is high it indicates an I/O operation andwhen it is low, it indicates a memory operation.

13. Ready: The READY signal is used to introduce wait state in microprocessor ifREADY = 0 then microprocessor ethers into wait state and if READY = 1

microprocessor does not enters into wait state.

14. CLKOUT: The CLK out signal is used to provide system clock to the external

devices.

The frequency of this signal is same as the frequency of crystal present on X1, X2

pins, i.e., 3.14 MHz.


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15. HOLD, HLDA: The HOLD signal is used to transfer

microprocessor in the HOLD state. If HOLD = 1 thenmicroprocessor enters into HOLD state and it gives logic 1

on HLDA pin (HOLD acknowledge).

In HOLD state microprocessor losses the control over address lines, data lines,control lines and these lines are now used by 8237 DMA controller.

16. Power Supply Pins (VCC, GND): The microprocessor 8085 has single VCC pin and

single GND pin. The VCC is connected to +5 volt and similarly GND is connected

to system GND.

IO/MRD

WR Operation

0 0 1 Memory reading

0 1 0 Memory writing1 0 1 I/O reading

1 1 0 I/O writing

1.4 ARCHITECTURE OF INTEL8085 OR BLOCK DIAGRAM

SID SOD

Serial I/Ocontrol

Interruptcontrol

RST 5.5RST 6.5RST 7.5

8 bit data bus

Accumulator(8)

Temporary(8)

Flag(8)

IR(8)

ALU(8)8

8

8 8 8 8 8

8

ID256

8

W(8) Z(8)

B(8)

D(8)

H(8)

C(8)

E(8)

L(8)

SP(16)

PC(16)

INC/DEC (16)

8

16

Addressbuffer

8

Address/Data buffer

8

A - A15 8 AD - AD7 0

8

256

Timing and controlunit

X1

X2

ALE RD WR V

(+5V)CC GND

(+5V)

Controlsignal

RST 4.5

TRAP

INTR

INTA

Figure 1.3

HLDA:HoldAcknowledgement

BTE [S-2010] 6M

Draw the blockdiagram of 8085

microprocessor.

Explain the functionof instruction register,

program counter andstack pointer.


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The microprocessor (microprocessor) 8085 is 40 pin NMOS family IC whose internal

circuit is made of 6200 transistors. The internal Block diagram of microprocessor 8085 isknown in figure.

1.4.1 Bus

A bus is a collection of conducting path which is used to transfer signal from one

functional unit to another functional unit. The microprocessor 8085 has three types ofbuses.

i. Address bus

ii. Data bus

iii. Control bus

are only used by microprocessor and user is not allowed to use these register.

1.4.2 ALU (Arithmetic Logical Unit)

ALU stands for arithmetic and logical unit. The ALU of microprocessor 8085 is 8-bit

microprocessor.

The ALU is responsible to perform all arithmetic and logical operation like addition,

subtraction, comparison, ANDING, etc.

1.4.3 Register Organization

a. Accumulator (ACC): The accumulator is 8-bit register

which contains 8 flip flops. Hence it can storemaximum 8-bit data.

The importance of accumulator is that, whenever

microprocessor performs any arithmetic or logical

operation in ALU then first 8-bit number is always

transferred from accumulator and result is stored backto the accumulator.

b. Temporary Register: (TEMP, W, Z): Themicroprocessor 8085 has three 8-bit temporary registersas temp W, Z. These registers are only used bymicroprocessor and user is not allowed to use these

register.

c. General Purpose Register: The microprocessor 8085

has six 8-bit general purpose registers as B, C, D, E, H

and L. These registers can be used to store any 8-bit

user data.

Register organization

i. Accumulator

ii. Temporary register(W, Z, Temp)

iii. General purpose

Register (B, C, D, E,

H, L)

iv. Stack Pointer (SP)

v. Program Counter(PC)

vi. Inc/Dec Register

vii. Flag Register

BTE [S-2011 1M]Describe the register

organization of 8085

microprocessor.


9/16


For storing a 126 bit number, we have to make pairs of two 8-bit registers like, BC,

DE and HL.

d. Stack Pointer (SP): The stack pointer is a 16-bit register which is used to store the

16-bit address of stack memory. It is used as a memory pointer. It points to a

memory location in R/W memory called as a stack.

The beginning of the stack is defined by loading a 16-bit address in the stackpointer. Stack Pointer (SP) points current top of stack.

e. Program Counter (PC): The program counter is 16 bit register which is used to

store 16 bit address of memory during the execution of program. The function of

program counter is to point to the next byte of instruction is to be fetched. When the

byte is being fetched, the program counter is automatically incremented by one topoint the next memory location.

f. INC/DEC Register: Increment/Decrement: It is a 16-bit register used to incrementor decrement the contents of program counter and stack pointer.

g. Flag Register: The flag register of microprocessor 8085 is of 8-bit which contains 8flip-flop, hence it can store maximum 8-bit data.

SF

D7 D6

ZF X AC PFX X CF

D5 D4 D3 D2 D1 D0

CarryflagParityflagAuxillarycarry flagZeroflagSignflag

Figure 1.4: Flag register format of 8085 microprocessor

The flag register contains following five different flags.

i. Carry Flag (CF):Whenever microprocessor performs addition of two 8- bit

numbers then the carry generated after the addition of entire 8-bit number is

directly copied into carry flag.

Similarly whenever microprocessor performs the subtraction of two 8-bit

numbers then borrow required for subtraction is directly copied into carryflag.

ii. Parity Flag (PF): The count of logic 1 in 8-bit result is called a s parity.

If the count of logic 1 in 8-bit result is an even No. i.e. 0/5/2/4/6/8/ then the

parity is even and PF = 1.

Similarly if the count of logic 1 in 8-bit result is an odd number i.e. 1/3/5/7/

then it is an odd parity and PF = 0.

iii. Auxillary Carry Flag (AC): The auxillary carry flag is also known as

intermediate carry or half carry.


10/16


Whenever microprocessor performs addition of two 8-bit numbers then the

carry generated after the addition of four LSBs is directly copied into AC flag.

Similarly whenever microprocessor performs the subtraction of two 8-bit

numbers then borrow required by 5 LSBs is directly copied into AC flag.

iv. Zero Flag (ZF): If the result obtained is completely zero, i.e., all 8-bits of resultis zero then ZF = 1.

But if the result obtained is non-zero then ZF = 0.

v. Sign Flag (SF): This sign flag is only used for signed binary numbers. If theresult obtained is negative number then SF = 1. But if the result obtained is a

positive number then SF = 0.

h. Instruction Register (IR)

IR

(8)

ID

86256

256

Timing and

Control

unit

The Instruction Register is an 8-bit register which is used to store 8-bit opcode ofthe instruction fetched from memory.

The opcode present in IR is then transferred to instruction decoder.

The instruction decoder has 8 input and 256 output lines. The ID decodes the 8-bit

opcode of 8-bit each instruction so as to general 256 bits micro codes or micro

instruction.

1.4.4 Instruction Decoder (ID)

It accepts an op. code of the instruction from the instruction register decode it and giveinformation to control logic. The information include what operation is to be performed

who is going to perform, how many operand bytes the instruction has, etc

1.4.5 Timing and Control Unit

The timing and control unit accepts information from the instruction decoder and

generates different control signal. This unit synchronizes all the microprocessor

BTE [S.2010] 6M

Describe function of8085

i. ALU

ii. Timing andcontrol unit

iii. InstructionRegister


11/16


operation and generates control and status signal necessary for communication between

the microprocessor and peripherals.

1.4.6 Interrupt Control UnitThe 8085 microprocessor includes four maskable interrupts and one non-maskable

interrupt. The microprocessor can ignore or delay a maskable interrupt request if it is

performing some critical task. However it has to respond to a non-maskable requestimmediately.

Maskable Interrupts

INTR Interrupt Request- priority 5

RST 7.5 Restart Interrupt priority 2

RST 6.5 Restart Interrupt priority 3

RST 5.5 Restart Interrupt priority 4Non-Maskable Interrupt TRAP Priority - 1

Whenmicroprocessor is executing a program it checks the INTR or any other interrupt

signal during the execution of each instruction.

If any signal is high the microprocessor completes the current instruction or executes the

interrupt service routine.

For INTR interrupt microprocessor sendsINTA signal as an acknowledgement to INTR

request. RST are the vectored interrupts. During the execution of these interrupts

program control to automatically transferred to specific location in memory without anyexternal hardware.

TRAP is non-maskable interrupt known as NMI. It has highest priority. It need not be

enables and it cannot be disabled.

1.4.7 Serial I/O Control Unit

The 8085 microprocessor has two pins specially designed for software controlled serial

I/O data transmission. Data transfer is controlled through two instructions RIM and SIM.

RIM instruction is used to input serial data through SID line whereas SIM instruction isnecessary to output data serially from SOD line.

1.4.8 Address/Data Buffer

Buffers are commonly used to increase the driving capability of dada bus and address

bus.


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1.5 8085 SYSTEM BUS

A bus is a collection of conducting path which are used to transfer signal from one

functional unit to another functional unit.

The microprocessor 8085 has following types of buses.

i. Address Bus: The microprocessor 8085 has 16-bit address bus from A15-A8 and

AD7AD0. The address bus id used to transfer 16 bit address of memory as well as 8-

bit address of I/O ports.

ii. Data Bus: The microprocessor 8085 has 8-bit data bus from AD4-AD0. These lines

are often known as well as multiplexed lines and time shared lines.

The AD7-AD0 are used to transform both addresses as well as data. But the addressand data is not transferred simultaneously so these lines are often known as time

shared lines.

iii. Control Bus: The microprocessor 8085 has 3 control buses as IO/M,

RD,

WR .

The IO/M is used to define operation either of memory or I/O ports. The

RD and

WR is used during reading and writing operation respectively.

1.6 DEMULTIPLEXING OF AD0-AD7 OF 8085

In the 8085 microprocessor the higher address lines, i.e., A8 - A15 are directly available,

but the lower order address lines are multiplexed with data bus in time sharing.

Hence, the de-multiplexing of address/data bus is required, i.e. separation of address

and data bus.

In microprocessor 8085, AD7-AD0 pins are used to transfer 8 LSBs of address as well as 8-bit

data. Practically AD7-AD0 pins are separated or demultiplexed using 8-bit internal latch(IC 8212).

When microprocessor will transfer 16 bit address on A15- A8 and AD7-AD0 pins, then at

the some time When microprocessor will give ALE = 1 (Address latch enable).

When ALE = 1, then latch IC is enabled. So LSBs of address on AD7-AD0 pins is storedin this latch. So address is continuously available on A15-A8 and A7-A0.

When microprocessor will transfer 8-bit data on AD7-AD0 pins then When microprocessor

gives ALE = 0. So latch IC is disabled and the 8-bit is not stored in the latch and data is

available on data line D0-D7.


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AD - AD7 0

A - A15 8

ALE

8

P

8085

8 bitlatch IC

8212

VCC 8

8A - A15 8

D - D7 0

A - A7 0

8

+5 V

GND

Figure 1.5: Demultiplexing of address data pins of 8085

1.7 LIMITATION OF 8085 MICROPROCESSOR

i. The 8085 is on 8-bit microprocessor hence it can perform operation only on two 8-

bit numbers.

ii. The 8085 has 16 bit address lines and 8-bit data lines.

iii. The 8085 can address maximum memory of 64 kB (216).

iv. The 8085 cannot perform any operation on ASCII number.

v. The 8085 cannot perform multiplication and division of numbers.

vi. The 8085 cannot perform subtraction, multiplication and division of BCD number.

vii. The 8085 cannot transfer the data directly from one memory to another memory.

viii. The 8085 can only address 256 I/O ports.

ix. The 8085 cannot perform the pipelining of instruction.

x. The 8085 microprocessor there is no provision to determine whether the resultobtained is within the limit of 8/16 bit number.


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Summary Microprocessor is an electric device which is made up of silicon technology and can compute

mathematical and logical operations.

8085 microprocessor 8-bit ALU so it is called 8-bit microprocessor and at a time only 8-bit dataprocesses. It is 40 pin IC.

8085 has 16 bit address lines and 8-bit data lines.

Internal Architecture of 8085 microprocessor includes

ALU (Arithmetic and Logical Unit)

Timing and control unit

Instruction register and instruction decoder (IR and ID)

Register Array

8085 has

a. 6 general purpose register

B, C, D, E, H, L

b. Accumulator

c. Program Counter (PC)

d. Stack Pointer (SP)

e. Temporary register (W, Z, temp)

Interrupt control unit (Hardware and software interrupt)

Serial I/O control

Address and Data Buffer

Flag Register

ALE is used to demultiplex the address and data signal.


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Exercise ____________________________________1. State the function of program counter and stack pointer of 8085. (Refer 1.4) 2M

2. State the function of following of 8085: (Refer 1.4) 4Mi. Accumulator

ii. Temporary Register

iii. Flag Register

iv. ALU

3. List maskable and non-maskable interrupts of 8085 microprocessor. (Refer 1.3) 2M

4. Describe the function of following block of 8085. (Refer 1.4) 6M

i. ALU

ii. Timing and control unit

iii. Instruction Decoder

5. Explain de-multiplexing of address and data bus in 8085. (Refer 1.6) 6M

6. State limitation of 8085 microprocessor. (Refer 1.7) 2M

7. Draw neat labeled architecture of 8085 indicating different. (Refer 1.4) 6M

8. List all registers of 8085 microprocessor and categorize them into 8 and 16 bit

register. (Refer 1.4) 4M


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BTE Questions________________________________[S.11 - 8M]

[W.10 - 6M]

[S.10, W.10 - 2M]

[S.10 - 6M]

[SP - 6M]

[SP - 2M]

[SP - 4M]

1. Describe the register organization of 8085 microprocessor.

(Refer 1.4)

2. Describe the function of following block of 8085. (Refer 1.4)

i. ALU

ii. Timing and control unit

iii. Instruction decoder

3. Describe evolution of microprocessor with suitable

example.

4. Draw the block diagram of 8085 microprocessor. Explainthe function of instruction register, program counter and

stack pointer. (Refer 1.4)

5. Explain Flag Register of microprocessor. (Refer 1.4)

6. Explain system bus of 8085 microprocessor. (Refer 1.5)

7. Explain De-multiplexing of address and data bus? (1.6)

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Microprocessor Intrpduction