8085 microprocessor

Evolution of MicroprocessorThe first microprocessor designed by Intel corporation in 1971 which first 4-bit microprocessor.The name of this microprocessor is 4004.It was the designed with 2300 transistors.It was designed by using large scale integration (LSI) technology.It has 640 bytes of memory addressing capacity.The “Jordon Moore” co-founder of Intel corporation,pridected that the number of transistors per integrated circuit would be double after every “18 months", this came to known as Moor’s Law.

Evolution of Microprocessor

• Intel Microprocessor is divided into following groups.

1. 4-bit Microprocessor-4004.

2. 8-bit Microprocessor-8008,8080,8085.

3. 16-bit Microprocessor-8086,8088,80286.

4. 32-bit Microprocessor-80386,80486,pentium.pentium pro,pentium-II,pentium-III,pentium-IV


Intel M.processor

Year of introducing

No. of transistor

Initial clock speed

Address BUS

Data BUS

(Word length)

Addressable Memory

Other Companies Processor

No of Bit M.processor

4004 1971 2,300108 KHz

10 Bit 4 Bit 640 bytes

Rockwell International

PPS-4-bit MP

4-Bit M.processor

8008 1972 3,500200 KHz

14 Bit 8 Bit 16 Kbytes

Zilog’s (Z-80, Z-800) Motorola’s (6800,6809)

8-Bit M.processor

8080 1972 60002

MHz16 Bit 8 Bit 64 Kbytes

8085 1976 6,5005

MHz16 Bit 8 Bit 64 Kbytes


Intel M.processor

Year of introducing

No. of transistor

Initial clock speed

Address BUS

Data BUS

(Word length)

Addressable Memory



8086 1978 29,000 5 MHz 20 Bit 16 Bit 1 MB

Zilog’s (Z-

8000) Motorola (68000, 68010)

16-Bit M.processor

8088 1979 29,000 5 MHz 20 Bit

16 Bit /8-

bit intern

al

1 MB

80286 1982 134,000 8 MHz 24Bit 16 Bit 16 MB


Intel M.processor

Year of introducing

No. of transistor

Initial clock speed

Address BUS

Data BUS

(Word length)

Addressable Memory



80386 1985 2,75,00016

MHz32Bit 32 Bit 4 GB

Zilog’s

(Z-80000) Motorola (68020, 68030)

32-Bit M.process

or

80486 19891.2

Million25

MHz32 Bit 32 Bit 4 GB

Pentium 19933.1

Million60


Pentium- Pro

19955.5

Million150


8085 Microprocessor Introduction:-The microprocessor is the central processing

(CPU) of microcomputer.

It is also known heart of computer or Brain of computer. It designed on single chip or IC (Integrated circuit). Microprocessor is also known as programmable digital

device, designed with registers, flip-flop and timing element.

It is also defined as multipurpose,programmable,clock driven, register based electronic device, that reads the instructions from storage device called memory, accepts the binary data as input & process the data according to instructions & provide the result.

8085 Microprocessor• The Intel 8085 is the 8-bit microprocessor

developed by Intel corporation in year 1976.

• It known as 8-bit Microprocessor because it can process 8-bits at a time.

• If the processor consists of more than 8-bits the processor takes up 8-bits of data at first & makes its processing, then next group of data taken up one by one.

Features of 8085 Microprocessor

1.Intel 8085 is 8 bit microprocessor. 2.It is developed by Intel corporation in 1976. 3.It has 40 pins IC (Integrated circuit ) fabricated on

single chip. 4.Its clock speed is 3 to 5 MHz. 5.The Intel 8085 uses a single +5 V D.C. supply for

its operation. 6.It is designed by using 6200 to 6500. 7.It has 8-bit data Bus. 8.It has 16 bit address.

Features of 8085 Microprocessor 9.It has16 bit address lines, therefore it can access 16

2 = 64 Kbytes of memory locations.

10.It has 8-bit I/O Addresses, 8 2 = 256 (0---255) ports can be accessed.

11. It has 80 basic instructions & 246 opcodes.Note : opcode means operational codes every instruction having a

code which is stored in memory.MVI A,05 is instruction, the meaning of this instruction is to transfer

05 data in to accumulator.MVI A ,05 ( in coded form 3E,05) where 3E is the opcode of

instruction & 05 is 8-bit data)

Pin Diagram & Description of 8085 Microprocessor

VSS AD0-AD7

Vcc

X1

X2 A8-A15

RESET IN CLK

RESET OUT HOLD

IO/M HLDA

S0 TRAP

S1 RST 7.5

RD RST 6.5

WR RST 5.5

ALE INTR

SID

SOD INTA

READY

INTEL

8

0

8

5


The 8085 microprocessor has 40 pin IC. Pin configuration is as follow. 1.AD0 –AD7 :This is the multiplexed &

bidirectional Bus. It is used as address as well as data Bus. The lower 8-bits address (A0—A7) is multiplexed

with data Bus (D0—D7).

2.A8- A15 : This is higher order Bus ,higher order addresses (A8-A15) sending through this bus

It 8 bit higher order or most significant bits (A8-A15) sending on this bus.


3.ALE : (Address latch Enable) Output It is active high signal. It controls the multiplexed bus AD0-AD7. When ALE goes high the Bus AD0-AD7 is used as address Bus

i.e. (A0-A7). When ALE goes low the Bus AD0-AD7 is used as data Bus. 4. IO/M (output pin) : It is status signal which distinguishes whether the address is for

memory or I/O. When it goes high address on the address bus is for I/O IO/M = High -- Address for I/O IO/M = Low -- Address for Memory


S0 /S1 (output) :These are status signal sent by the microprocessor to distinguish various types of operation given in table.

S1 S0 Operations 0 0 HLT 0 1 WRITE 1 0 READ 1 1 FETCH RD (Output) : This signal is used to control READ operation. When it goes low the memory or I/O device is read.

WR ( Output) : This signal is used to control WRITE operation When it goes low data is written into the selected memory or I/O .


READY (Input): This signal is used by microprocessor to check peripheral is ready to transfer the data or not.

A slow peripherals may be connected through this line or pin.

HOLD (Input) : Another devices or I/O devices requesting to the processor for the use of data & address Bus.

HLDA (Output) : Acknowledgement This is acknowledgement pin . The processor sends acknowledgement (permission) to the

requesting device that processor is ready to accept the request.


INTR (Interrupt) Input : It is an interrupt request signal. INTA (Output): If processor is ready to accept the

request then sends acknowledgement signals. Note :Interrupts are signals that cause the computer’s

CPU to suspend what is to be doing & transfer to special program called Interrupt handler.

When interrupt signal occurs at that time processor stops his main program & transfer towards special programs, the processor executes this subprogram given by interrupt signals & returns towards main program.


RST 7.5,RST 6.5,RST 5.5 and TRAP : These interrupt signals. Other peripheral devices or co-processors interrupt through this

signals or pins. TRAP has highest priority.

RESET IN : This is active low signal used to reset microprocessor.

When this signal is received by the microprocessor,miroprocessor clears program counter i.e. 0000.

RESET OUT (Output): It is active high output signal. It indicates that processor is being reset.


• X1,X2 (Input) :These are clock input pins connected to crystal oscillator

• Which drives an internal circuit of microprocessor to produce suitable clock, for operation of the microprocessor.

• CLK (Output):• It is clock output for user can be used for other digital

IC’s.• It’s frequency is same at which processor operates.• Internal operating frequency of microprocessor is

available on this pin & used to operate other devices in the system with speed.


• SID & SOD :Serial input data & serial output data• SID pin is used to accept one bit data under software

control.

• VCC : Vcc provides +5v supply for the operation of microprocessor.

• VSS : Ground reference.

8085 Microprocessor Architecture or Block diagram of 8085

• The Block diagram of Intel 8085 consists of following three main sections.

• 1.Arithematic and Logic unit (ALU)

• 2.Timing & control unit

• 3.Set of Registers


INTR,RST 7.5,RST 6.5,RST 5.5 ,TRAP SID SOD

INTA

Interrupt control Serial input/output

ACCUMULATORTEMP.

REGISTERFLAG

REGISTER

ALU

TIMING & CONTROL

INSTRNREGISTER

INSTRN DECODER

& M/C CYCLE

ELCODING

ADDRESSBUFFER

ADDR./ DATA BUFFER

W Z B C D E H L Stack Pointer

Prog. CounterIncr./DecreAddr.Latch

A15-A8AD7-AD0


• 1.Airtematic & Logic control : (ALU)

• ALU is the main part of microprocessor which performs arithmetic & logic operations

• Arithmetic operation like addition subtraction.• The logical operations like

AND,OR,NOT,Increment,decrement,shift,rotate.• It takes data from accumulator & temporary

register & stores the result in accumulator.• ALU is combinational circuit which consists of

adder, AND gate, OR gate & NOT gate.


• 2.Timing and control Unit :-• The timing & control unit is section of CPU.• It generates timing & control signals which are necessary

for the execution of instructions.• It controls data flow between CPU & peripherals (including

memory ).• It performs data transfer & decision making operations.• It consists of instruction register, instruction decoder,

timing & control circuit.• It control entire operation of microprocessor & peripherals

connected to it.


• 3.Register Organisation:Resgisters are used by microprocessor for temporary storage of data & instructions.

• These registers are known internal memory of M.processor.

• The 8085 has following registers :-

• 1] One 8-bit accumulator (ACC) or Reg. A

• 2] Six 8-bit general purpose registers these are B,C,D,E,H,L.

• 3] One 16-bit stack pointer (SP)

• 4] One 16-bit program counter (PC)

• 5] Instruction register

• 6.Temporary Register


• 1] One 8-bit accumulator (ACC) or Reg. A :-• Accumulator is 8-bit registers.• It is also known as Reg.A.• It is used to hold one of the operand (data) of an

arithmetic & logical operation.• The another operand (Data) for arithmetic & logical

operations may stored in memory or one of the register.

• It is used as input device to ALU.• Finally result is stored in the accumulator.


• 2] General purpose registers :-

• The 8085 has 6 general purpose 8 bit registers B,C,D,E,H,L.

• These registers available for the user.

• These registers used to store 8-bit data.

• The pair of two registers can be used as 16-bit registers these pairs are BC,DE,HL.


• 3] Stack pointers (SP) :-• It is special purpose register.• It is used to access stack memory.• It always used to point to the stack memory.Note :-Stack Memory : The stack is a sequence of memory

locations set aside by programmer to store the contents of accumulator,flags,program counter,& general purpose Reg.during execution of program.

• Some part of RAM memory is used as stack.• During the execution of the program some times it becomes

necessary to save contents of some registers which are need for some other operations,in subsequent steps of the program.

• The contents of such registers saved in the stack.


• 4.Program counter : (PC)• Program counter is 16-bit special purpose Register.• It is always used to hold the address of program

memory.• It gives the track of memory addresses of the

instructions in the program while they are being executed.

• It never hold operands or data • It is automatically incremented by control unit during

instruction fetch operations.• During instruction fetch operation a 8085

microprocessor places contents of PC on address bus to select appropriate location of program memory.


• 5.Instruction Register :-• The instruction register holds the opcode (Operation

code or instruction code ) of the instruction which being decoded & executed.

• It is 8-bit register.• It is not available for user.• 6] temporary Register :-• It is 8-bit register associated with temporary.• It is not available for user.• It holds data during an arithmetic / Logical Operation• It is used by the microprocessor.


• Flag Register :-

• It is available for user.

• The ALU stores the status of result in the flag registers.

• The ALU includes five flip-flops which are set or reset after an operation according to condition of result.

• These flag registers are known as flags.• There are five flags of 8085 M.processor. ( carry

flag,Auxillary carry flag, parity flag, Zero flag, sign flag )

• These flag registers are connected to ALU.


• Flag structure of 8085 or Program status word of 8085

MSB LSB

Zero Flag Parity Flag Carry Flag

• Sign Flag Auxillary Carry Flag

D7 D6 D5 D4 D3 D2 D1 D0

S Z X AC X P X CY


• 1] Carry Flag ( CY or CF) :-• After execution of instruction carry is generated ,carry flag

set to ‘1’ otherwise reset to ‘0’.

• 2] Auxillary carry Flag (AC) :-• If carry is generated from bit 3 to bit 4 (D4-D3) ,it is set to

‘1’ otherwise reset to ‘0’.

• 3] Parity Flag (P) :-• If result of operation contains even number of ‘1’ the parity

flag is set to’1’ ,or result of operation contains odd no.of ‘1’,the parity flag reset to ‘0’.


• 4] Zero Flag :-• If result of operation is zero (0), then zero flag is set

to ‘1’ otherwise non zero result reset to ‘0’.

• 5] Sign Flag (S) :-• The sign flag ‘S’ set to 1 ,if the result of operation is

negative.• It is always used in signed arithmetic operation.• In logical operation MSB is 1 the sign flag is set to1.


• Applications of microprocessor :-

• 1.Microprocessor are used in controllers, personal computers, low to moderate speed data communication.

• 2. microprocessor used as digital controller to control some physical parameters like temperature, pressure.

• 3.It is used to control motor speed, traffic light controller, conveyer controls, stepper motor controller.

• 4.It is used in data communication application applications including data processing error detection, serial to parallel & parallel to serial data transfers.


• 5.It is used in personal computer.

• 6.Microprocessor are also used in automobils,applications are ignition control, automatic fuel control.

• 7.Microprocessors are used in many medical instruments like X-ray machines,ECG machines.

8.Microprocessors are used in testing & measuring instruments, applications are CRO’s,signal generator power supplies, spectrum analyzers.


• Limitations of 8-Bit microprocessor:-

• 1.The word length is 8-bit hence processing speed is low.• 2.Due to 16-bit address lines, we can address only up to 64

Kbytes of memory.• 3.8-bit microprocessor has multiplexed address & data bus,

so extra hardware is required to separate address signals.• 4.It can read one instruction at a time ,unless first

instruction gets executed completely, microprocessor can not read second instruction from memory as it has only one instruction register.

• 5.Operating speed is less so the speed of execution is low.


• 6.Using 8-bit microprocessor, we can not design multiprocessor system.

• 7. Due to limited size of the all register, we can store limited data bytes in the microprocessor memory.

• 8.There is no memory management unit.

• 9. It is used for control applications.

• 10. It is not used in work stations & servers.

8085 microprocessor

Documents

intel microprocessor

microprocessor introduction

data bus d0d7

processor year of

high address

bits of data

companies processor

initial address