Microprocessor Instruction Set

THE 8085 INSTRUCTION SET

Prepared By: Ajay Shah Asst. Prof., CE Dept ACET, Khatraj

WHAT IS A MICROPROCESSOR? The word comes from the combination micro and

processor. Processor means a device that processes whatever. In this context processor means a device that

processes numbers, specifically binary numbers, 0’s and 1’s. To process means to manipulate. It is a general

term that describes all manipulation. Again in this content, it means to perform certain operations on the numbers that depend on the microprocessor’s design.

Prepared By: Ajay Shah

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WHAT ABOUT MICRO? Micro is a new addition. In the late 1960’s, processors were built using

discrete elements. These devices performed the required operation, but

were too large and too slow.

In the early 1970’s the microchip was invented. All of the components that made up the processor were now placed on a single piece of silicon. The size became several thousand times smaller and the speed became several hundred times faster. The “Micro”Processor was born.


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DEFINITION OF THE MICROPROCESSOR

The microprocessor is a programmable device that takes in numbers, performs on them arithmetic or logical operations according to the program stored in memory and then produces other numbers as a result.


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DEFINITION (CONTD.) Lets expand each of the underlined words: Programmable device: The microprocessor can perform

different sets of operations on the data it receives depending on the sequence of instructions supplied in the given program. By changing the program, the microprocessor manipulates the data in different ways.

Instructions: Each microprocessor is designed to execute a specific group of operations. This group of operations is called an instruction set. This instruction set defines what the microprocessor can and cannot do.


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DEFINITION (CONTD.) Takes in: The data that the microprocessor

manipulates must come from somewhere. It comes from what is called “input devices”. These are devices that bring data into the system

from the outside world. These represent devices such as a keyboard, a

mouse, switches, and the like.


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DEFINITION (CONTD.) Numbers: The microprocessor has a very narrow view

on life. It only understands binary numbers.

A binary digit is called a bit (which comes from binary digit).

The microprocessor recognizes and processes a group

of bits together. This group of bits is called a “word”.

The number of bits in a Microprocessor’s word, is a measure of its “abilities”.


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DEFINITION (CONTD.) Words, Bytes, etc.

The earliest microprocessor (the Intel 8088 and Motorola’s 6800) recognized 8-bit words. They processed information 8-bits at a time. That’s why they are

called “8-bit processors”. They can handle large numbers, but in order to process these numbers, they broke them into 8-bit pieces and processed each group of 8-bits separately.

Later microprocessors (8086 and 68000) were designed with 16-bit

words. A group of 8-bits were referred to as a “half-word” or “byte”. A group of 4 bits is called a “nibble”. Also, 32 bit groups were given the name “long word”.

Today, all processors manipulate at least 32 bits at a time and there

exists microprocessors that can process 64, 80, 128 bits or more at a time.


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DEFINITION (CONTD.) Arithmetic and Logic Operations:

Every microprocessor has arithmetic operations such as add and subtract as part of its instruction set. Most microprocessors will have operations such as multiply

and divide. Some of the newer ones will have complex operations such as

square root.

In addition, microprocessors have logic operations as well. Such as AND, OR, XOR, shift left, shift right, etc.

Again, the number and types of operations define the microprocessor’s instruction set and depends on the specific microprocessor.


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DEFINITION (CONTD.)

Program: A program is a sequence of instructions that bring data into the microprocessor, processes it and sends it out.

There are many programming languages (C, C++,

FORTRAN, and JAVA…) However, these programming languages can be grouped into three main levels (these days a fourth level is developing).


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DEFINITION (CONTD.) Programming Languages

Machine language Machine language is the lowest level programming

language. It is a language intended to be understood by the microprocessor (the machine) only. In this language, every instruction is described by binary patterns.

e.g. 11001101 may mean 1 + 2 This is the form in which instructions are stored in

memory. This is the only form that the microprocessor understands.


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Assembly language This language is more understandable by humans. In

this language, the binary patterns are assigned mnemonics (short abbreviated names).

e.g. “Add 1,2” is assigned to the machine language pattern 11001101 mentioned above to refer to the operation 1+2.

There is usually one assembly language instruction for

each machine language instruction.


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High level languages These are languages like C, PASCAL and FORTRON. These

are more natural for humans to use than assembly or machine languages. They are also more compact (i.e. it takes less statements to write the program).

One high level instruction translates into many assembly or machine language instructions.

e.g. x = y + z may translate into: MOV 1000, R1 MOV 1004, R2

ADD R1, R2

MOV R1, 1008 Prepared By: Ajay Shah

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DEFINITION (CONTD.)

Programming Languages The new level being developed: is ultra high level

languages which would contain things like C++, and JAVA. Here a single instruction may translate into

hundreds of assembly or machine language instructions.


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DEFINITION (CONTD.) Stored in memory :

First, what is memory? Memory is the location where information is kept while not

in current use. Memory is a collection of storage devices. Usually, each

storage device holds one bit. Also, in most kinds of memory, these storage devices are grouped into groups of 8. These 8 storage locations can only be accessed together. So, one can only read or write in terms of bytes to and form memory.

Memory is usually measured by the number of bytes it can hold. It is measured in Kilos, Megas and lately Gigas. A Kilo in computer language is 210 =1024. So, a KB (KiloByte) is 1024 bytes. Mega is 1024 Kilos and Giga is 1024 Mega.


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DEFINITION (CONTD.) Stored in memory:

When a program is entered into a computer, it is stored in memory. Then as the microprocessor starts to execute the instructions, it brings the instructions from memory one at a time.

Memory is also used to hold the data. The microprocessor reads (brings in) the data from memory

when it needs it and writes (stores) the results into memory when it is done.


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DEFINITION (CONTD.) Produces: For the user to see the result of the execution

of the program, the results must be presented in a human readable form. The results must be presented on an output device.

This can be the monitor, a paper from the printer, a simple LED or

many other forms.


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A MICROPROCESSOR-BASED SYSTEM From the above description, we can draw the following block diagram to represent a microprocessor-based system:

Memory

Output Input


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INSIDE THE MICROPROCESSOR Von Neumann Architecture:

Share memory for program and data with one data bus and one address bus between processor and memory.

Instruction and data have to be fetched in sequential order, limiting the operation bandwidth.

The 8085 follows the von Neumann architecture with a 16 bit address bus and 8 bit data bus.

Harvard Architecture:

Uses physically separate memories for instruction and data, requiring dedicated buses for each of them.

Instruction and operands can be fetched simultaneously.

Internally, the microprocessor is made up of 3 main units.

The Arithmetic/Logic Unit (ALU) The Control Unit. An array of registers for holding data while it is being

manipulated. Design of the harvard architecture


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ARITHMETIC LOGIC UNIT

Is the area of microprocessor where various computing functions are performed on data such as addition, subtraction, logic operations (AND, Or and exclusive OR).


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REGISTER ARRAY This area of μp identified by letters such

as B, C, D, E,H and L. Used to store data temporarily during the

execution of a program and are accessible to the user through instructions.


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CONTROL UNIT Provides the necessary timing and control

signals to all the operations in the microcomputer.

Control the flow of data between μp and memory and peripheral.


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MEMORY Two types of memory: ROM (read only memory) RAM ( random access memory)


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INPUT/OUTPUT Used to communicate with the outside world. The I/O device is knows as peripherals. Input devices: Keyboard Switches ADC

Output devices: LED DAC LCD


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THE 8085 PROGRAMMING MODEL Registers:

6 general purpose registers to store 8 bit data (B, C, D, E, H, L) Can be combined as registers pairs-BC, DE and HL – to perform 16 bit operations To store or copy data into registers

Accumulator: The Accumulator is an 8-bit register that is part of arithmetic/logic unit(ALU) Used to perform arithmetic and logic operations and the result is stored in the accumulator and also called register A Stack pointer, SP, is an 16-bit register, which contains the address of

the top of the stack. Prepared By: Ajay Shah

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THE 8085 PROGRAMMING MODEL (CONTD.) Flags: The ALU includes five flip-flops, which are set or

reset after an operation according to data conditions of the result in the accumulator and registers.

Used for decision making process of the microprocessor

S – Sign flag –D7 Z – Zero flag – D6 AC – Auxiliary Carry flag – D4 P – Parity flag – D2 CY – Carry flag – D0


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THE 8085 PROGRAMMING MODEL (CONTD.) The sign flag, S, indicates the sign of a value calculated by an

arithmetic or logical instruction. The zero flag, Z, is set to 1 if an arithmetic or logical operation

produces a result of 0;otherwise set to 0. The parity flag, P, is set to 1 if the result of an arithmetic or

logical operation has an even number of 1’s; otherwise it is set to 0.

The carry flag, CY, is set when an arithmetic operation generates

a carry out. The auxiliary carry flag, AC, very similar to CY, but it denotes a

carry from the lower half of the result to the upper half. Prepared By: Ajay Shah

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THE 8085 PROGRAMMING MODEL (CONTD.)

The Program Counter (PC): This is a register that is used to control the sequencing of the

execution of instructions. This register always holds the address of the next instruction. Since it holds an address, it must be 16 bits wide.

The Stack pointer (SP): The stack pointer is also a 16-bit register that is used to point

into memory. The memory this register points to is a special area called the

stack. The stack is an area of memory used to hold data that will be

retreived soon. The stack is usually accessed in a Last In First Out (LIFO)

fashion.


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THE 8085 INSTRUCTIONS

An instruction is a binary pattern designed inside a microprocessor to perform a specific function

The entire group of instructions, called the instruction set, determines what functions the microprocessor can perform

The microprocessor performs a task by reading and executing the set of instructions, written in sequence, is called a program

Since the 8085 is an 8-bit device it can have up to 28 (256) instructions. However, the 8085 only uses 246 combinations that represent a total of 74

instructions. Most of the instructions have more than one format.

These instructions can be grouped into five different groups:

Data Transfer Operations Arithmetic Operations Logic Operations Branch Operations Machine Control Operations


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INSTRUCTION FORMATS Each instruction has two parts. The first part is the task or operation to be

performed. This part is called the “opcode” (operation code).

The second part is the data to be operated on

Called the “operand”.

Exa: MVI A,B


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OPERAND TYPES There are different ways for specifying the

operand: There may not be an operand (implied operand)

CMA The operand may be an 8-bit number (immediate

data) ADI 4FH

The operand may be an internal register (register) SUB B

The operand may be a 16-bit address (memory address) LDA 4000H


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INSTRUCTION SIZE Depending on the operand type, the

instruction may have different sizes. It will occupy a different number of memory bytes. Typically, all instructions occupy one byte only. The exception is any instruction that contains

immediate data or a memory address.

Instructions that include immediate data use two bytes.

One for the opcode and the other for the 8-bit data. Instructions that include a memory address occupy

three bytes. One for the opcode, and the other two for the 16-bit

address.


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8085 INSTRUCTION TYPES


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8085 INSTRUCTION TYPES (CONTD.)


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8085 INSTRUCTION TYPES (CONTD.)


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THE 8085 ADDRESSING MODES Addressing Modes is the technique used to fetch

the desired operand during the execution of an instruction.

Instructions can be categorized according to their method of addressing the hardware registers and/or memory.

The 8085 MPU uses five addressing Modes: 1.Immediate Addressing Mode 2. Register Addressing Mode 3. Direct Addressing Mode 4. Register Indirect Addressing Mode 5. Implied Addressing Mode


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THE 8085 ADDRESSING MODES (CONTD.) Immediate Addressing Mode: Data immediately follow the op code in program

memory. The operand comes from next byte in program

memory. The immediate instructions indicate immediate

data (add instruction is ADD - add immediate instruction is ADI)

Use 2 bytes instruction. Example: ADI 05H MVI A, 12H


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THE 8085 ADDRESSING MODES (CONTD.)

Register Addressing Mode: The operand is retrieved from internal CPU

Register Data is provided through the registers. Example: MOV A,D ADD H


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Direct Addressing Mode: Used to accept data from outside devices to store

in the accumulator or send the data stored in the accumulator to the outside device.

In this type address of data is directly provided as a part of instruction

Example: LDA 2050H IN 34H OUT 45H


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Register Indirect Addressing Mode: The instructions reference memory using the

content of a register pair. The instruction MOV M,C moves the contents of

the C register into the memory address stored in the H and L register pair.

Instruction specifies register pair containing address, where the data is located.

Example: MOV M,C ADD M


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Implied Addressing Mode: Certain Instructions is implied by the

instruction’s function. Not A real addressing modes. Example : STC (set carry flag) instruction deals only with the

carry flag, HLT


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Combined Addressing Mode: Some instruction combines more than one

addressing mode Example: CALL 2050H – Combines direct and indirect

addressing mode


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DATA TRANSFER OPERATIONS

Instruction Bytes M-cycle T-states Flags Example MOV Rd, Rs 1 1

F 4 None MOV B,C

MOV M, Rs 1 2 F W

7 None

MOV M, C

MOV Rd, M 1 2 F R

7 None MOV B,M

MOV - Copy from Source to Destination.


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MOV - Copy from Src to Dest.


Instruction Bytes M-cycle T-states Flags Example MVI Rd, Data 2 2

F R 7 None MVI B,3AH

MVI M, Data 2 3 F R W

10 None

MVI M,3AH

MVI – Move Immediate 8 bit.


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Instruction Bytes M-cycle T-states Flags Example LDA Addr16 3 4

F R R R 13 None LDA 2050H

LDA – Load accumulator direct


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Instruction Bytes M-cycle T-states Flags Example LDAX Reg. Pair 1 2

F R 7 None LDAX B

LDAX – Load accumulator Indirect


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Instruction Bytes M-cycle T-states Flags Example LXI Reg. Pair,16bit data

3 3 F R R

10 None LXI B,2050H

LXI – Load register Pair immediate


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Instruction Bytes M-cycle T-states Flags Example LHLD 16bit addr

3 5 F R R R R

16 None LHLD 2050H

LHLD – Load H & L direct


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Instruction Bytes M-cycle T-states Flags Example STA 16bit addr

3 4 F R R W

13 None STA 2050H

STA – store accumulator direct


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Instruction Bytes M-cycle T-states Flags Example STAX Reg pairB/D

1 2 F W

7 None STAX B

STAX – store accumulator Indirect


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Instruction Bytes M-cycle T-states Flags Example SHLD 16bit addr

3 5 F R R W W

16 None SHLD 2050H

SHLD – Store H & L Registers Direct


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Instruction Bytes M-cycle T-states Flags Example XCHG 1 1

F 4 None XCHG

XCHG – Exchange H & L with D & E


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Instruction Bytes M-cycle T-states Flags Example SPHL 1 1

S 6 None SPHL

SPHL – Copy H & L to stack pointer


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Instruction Bytes M-cycle T-states Flags Example XTHL 1 5

F R R W W

16 None XTHL

XTHL – Exchange H & L with top of the stack


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Instruction Bytes M-cycle T-states Flags Example PUSH Reg. pair

1 3 S W W

12 None PUSH B

PUSH – push register onto stack


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Instruction Bytes M-cycle T-states Flags Example POP Reg. pair

1 3 F R R

10 None POP H

POP – pop off stack to register pair


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Instruction Bytes M-cycle T-states Flags Example OUT 8bit addr 2 3

F R O 10 None OUT 45H

IN 8bit addr 2 3 F R I

10 None IN 0FH


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Instruction Bytes M-cycle T-states Flags Example ADD R 1 1

F 4 All ADD B

ADD M 1 2 F R

7 All ADD M

ARITHMETIC OPERATIONS


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Instruction Bytes M-cycle T-states Flags Example ADC R 1 1

F 4 All ADC B

ADC M 1 2 F R

7 All ADC M



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Instruction Bytes M-cycle T-states Flags Example ADI 8BIT 2 2

F R 7 All ADI 59H



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Instruction Bytes M-cycle T-states Flags Example ACI 8BIT 2 2

F R 7 All ACI 59H



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Instruction Bytes M-cycle T-states Flags Example DAD REG PAIR

1 3 F B B

10 CY

DAD B



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Instruction Bytes M-cycle T-states Flags Example SUB R 1 1

F 4 All SUB B

SUB M 1 2 F R

7 All SUB M


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Instruction Bytes M-cycle T-states Flags Example SBB R 1 1

F 4 All SBB B

SBB M 1 2 F R

7 All SBB M



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Instruction Bytes M-cycle T-states Flags Example SUI 8bit data 2 2

F R 7 All SUI 59H



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Instruction Bytes M-cycle T-states Flags Example SBI 8bit data 2 2

F R 7 All SBI 59H



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Instruction Bytes M-cycle T-states Flags Example INR R 1 1

F 4 All

EXCEPT CY

INR B

INR M 1 3 F R W

10 All EXCEPT CY

INR M


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Instruction Bytes M-cycle T-states Flags Example INX Reg. Pair

1 1 S

6 NONE INX B


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Instruction Bytes M-cycle T-states Flags Example DCR R 1 1

F 4 All

EXCEPT CY

DCR B

DCR M 1 3 F R W

10 All EXCEPT CY

DCR M


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Instruction Bytes M-cycle T-states Flags Example DCX Reg. Pair

1 1 S

6 NONE DCX B


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Instruction Bytes M-cycle T-states Flags Example DAA 1 1

F 4 ALL DAA


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LOGICAL OPERATIONS

Instruction Bytes M-cycle T-states Flags Example CMP R 1 1

F 4 ALL CMP B

CMP M 1 2 F R

7 ALL CMP M


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LOGICAL OPERATIONS

Instruction Bytes M-cycle T-states Flags Example CPI 8BIT DATA

2 2 F R

7 ALL CPI C2H


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LOGICAL OPERATIONS

Instruction Bytes M-cycle T-states Flags Example ANA R 1 1

F 4 ALL

ANA B

ANA M 1 2 F R

7 ALL ANA M


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LOGICAL OPERATIONS

Instruction Bytes M-cycle T-states Flags Example ANI 8BIT DATA

2 2 F R

7 ALL

ANI 20H


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LOGICAL OPERATIONS

Instruction Bytes M-cycle T-states Flags Example XRA R 1 1

F 4 ALL

XRA B

XRA M 1 2 F R

7 ALL XRA M


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LOGICAL OPERATIONS

Instruction Bytes M-cycle T-states Flags Example XRI 8BIT DATA

2 2 F R

7 ALL

XRI 20H


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LOGICAL OPERATIONS

Instruction Bytes M-cycle T-states Flags Example ORA R 1 1

F 4 ALL

ORA B

ORA M 1 2 F R

7 ALL ORA M


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LOGICAL OPERATIONS

Instruction Bytes M-cycle T-states Flags Example ORI 8BIT DATA

2 2 F R

7 ALL

ORI 20H


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LOGICAL OPERATIONS

Instruction Bytes M-cycle T-states Flags Example RLC 1 1

F 4 CY RLC


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LOGICAL OPERATIONS

Instruction Bytes M-cycle T-states Flags Example RRC 1 1

F 4 CY RRC


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LOGICAL OPERATIONS

Instruction Bytes M-cycle T-states Flags Example RAL 1 1

F 4 CY RAL


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LOGICAL OPERATIONS

Instruction Bytes M-cycle T-states Flags Example RAR 1 1

F 4 CY RAR


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LOGICAL OPERATIONS

Instruction Bytes M-cycle T –states Flags Example

CMA 1 1 F

4 NONE CMA

CMC 1 1 F

4 CY CMC

STC 1 1 F

4 CY STC


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CONTROL OPERATIONS

Instruction Bytes M-cycle T-states Flags Example NOP 1 1

F 4 None NOP

HLT 1 1

F 4 None HLT


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CONTROL OPERATIONS

Instruction Bytes M-cycle T-states Flags Example DI 1 1

F 4 None DI

EI 1 1

F 4 None EI


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CONTROL OPERATIONS

Instruction Bytes M-cycle T-states Flags Example RIM 1 1

F 4 None RIM


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CONTROL OPERATIONS

Instruction Bytes M-cycle T-states Flags Example SIM 1 1

F 4 None SIM


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REFERENCES 1.Microprocessor Architecture, Programming, and

Applications with the 8085 - Ramesh S. Gaonkar Pub: Penram International.


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Documents

Microprocessor Instruction Set