Instruction Set pec lecture

8/14/2019 Instruction Set pec lecture

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INTRODUCTION TO 8085 INSTRUCTION SET


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INTRODUCTION

A microcomputer performs a task by reading and executing the

set of instructions written in its memory.

This set of instructions, written in a sequence, is called a

program.

Each instruction in the program is a command, in binary, to the

microprocessor to perform an operation.


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DATA TRANSFER OPERATIONS

The data transfer instructions copy data from a sourceinto a destination without modifying the contents of thesource.

The previous contents of the destination are replaced bythe contents of the source.


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DATA TRANSFER OPERATIONS


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MACHINE CONTROL OPERATIONS


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EXAMPLE 1

Load the accumulator A with the data byte 82H (the letterH indicates hexadecimal number), and save the data inregister B.


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Instructions: MVI A, 82H,

MOV B,A

The first instruction is a 2-byte instruction that loads the

accumulator with the data byte 82H, and the secondinstruction MOV B,A copies the contents of the

accumulator in register B without changing the contents

of the accumulator.


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EXAMPLES

Get a data to accumulator and then move it to register B.

Load the content of memory location 200H directly to the

accumulator, then transfer it to the register B.


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Get a data to accumulator and then move it to register B. MVI A,05(data)

MOV B,A


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Load the content of memory location 200H directly to the

accumulator, then transfer it to the register B. LDA 2000H

MOV B,A


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ARITHMETIC AND LOGIC INSTRUCTIONSARITHMETIC AND LOGIC INSTRUCTIONS


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ARITHMETIC OPERATIONSARITHMETIC OPERATIONS

Addition,

Subtraction,

Increment,

Decrement.


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ADDITIONADDITION

Addition takes several forms in the 8085

microprocessor like 8-bit binary, 16-bit binary etc


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ADDITIONADDITION


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The contents of the accumulator are 93H andcontents of a register C is B7 H. Add both thecontents.


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ADDITIONADDITION


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Add the number 35H to directly to the sum in theprevious example when the CY flag is set.


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ADDITIONADDITION


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Write a program to perform the following functions, Load the number 8BH in register D.

Load the number 6FH in register C.

Increment the contents of register C by one.

Add the contents of register C and D and display the sum at theoutput PORT1.


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MVI D,8DH

MVI C,6FH

INR C

MOV A,CADD D

OUT PORT1

HLT


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SubtractionSubtraction

The 8085 supports 8-bit binary subtraction and decrement.The 8085 supports 8-bit binary subtraction and decrement. It also supports a subtraction instruction that allows a borrow to beIt also supports a subtraction instruction that allows a borrow to be

propagated through additional bytes of a number.propagated through additional bytes of a number.

The subtract-with-borrow instruction aids in the subtraction ofThe subtract-with-borrow instruction aids in the subtraction of

multiple-byte numbers. .multiple-byte numbers. .


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The 8085 performs subtraction by using the method

of 2s complement.Subtraction can be performed by using either: the instruction SUB to subtract contents of a source register or

the instruction SUI to subtract an 8-bit number from contents

of the accumulator. In either case, the accumulator contents are regarded as

minuend (the number from which to subtract).


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The 8085 performs the following steps internally to executeThe 8085 performs the following steps internally to execute

the instruction SUB (or SUI):the instruction SUB (or SUI): Step1:Converts subtrahend (the number to be subtracted)Step1:Converts subtrahend (the number to be subtracted)

into its 1s complement.into its 1s complement.

Step2:Adds 1 to 1s complement to obtain 2s complementStep2:Adds 1 to 1s complement to obtain 2s complement

of the subtrahend.of the subtrahend.

Step3:Add 2s complement to the minuend (the contents ofStep3:Add 2s complement to the minuend (the contents of

the accumulator).the accumulator).

Step4:Step4:

Complements the Carry flagComplements the Carry flag

::

The programmer can check whether the resultThe programmer can check whether the result

indicates the true magnitude by checking the CY flag.indicates the true magnitude by checking the CY flag.

If CY flag is reset the result is positive and if CY flagIf CY flag is reset the result is positive and if CY flag

is set, the result is expressed in 2s complement.is set, the result is expressed in 2s complement.


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Illustrative Program: Subtraction of Two NumbersIllustrative Program: Subtraction of Two Numbers

PROBLEM STATEMENTPROBLEM STATEMENT Write a program to do the following:Write a program to do the following:

Load the number 30H in register B and 39H in register C.Load the number 30H in register B and 39H in register C.

Subtract 39H from 30H.Subtract 39H from 30H.

Display the answer at PORT I.Display the answer at PORT I.


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PROGRAM DESCRIPTIONPROGRAM DESCRIPTION Registers B and C are loaded with 30H and 39H, respectively.Registers B and C are loaded with 30H and 39H, respectively.

The instruction MOV A,B copies 30H into the accumulatorThe instruction MOV A,B copies 30H into the accumulator

(shown as register contents).(shown as register contents).


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To execute the instruction SUB C the microprocessorTo execute the instruction SUB C the microprocessor

performs the following steps internally:performs the following steps internally:


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PROGRAM DESCRIPTIONPROGRAM DESCRIPTION The number F7H is a 2s complement of the magnitude (39H-The number F7H is a 2s complement of the magnitude (39H-

30H)=09H.30H)=09H.

This Cy flag is set, indicating the answer is in 2s complement.This Cy flag is set, indicating the answer is in 2s complement.

The instruction OUT displays F7 at PORT1.The instruction OUT displays F7 at PORT1.


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NOTNOT

The CMA instruction (2FH in machine language), ones-The CMA instruction (2FH in machine language), ones-

complements the contents of the accumulator.complements the contents of the accumulator.

This operation, which affects none of the flag bits, causesThis operation, which affects none of the flag bits, causes

each bit of the accumulator to be inverted (changed fromeach bit of the accumulator to be inverted (changed from

1 to 0 or 0 to 1).1 to 0 or 0 to 1).

The CMA instruction causes the accumulator to appear asThe CMA instruction causes the accumulator to appear as

eight inverters (or NOT).eight inverters (or NOT).


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LOGIC INSTRUCTIONSLOGIC INSTRUCTIONS

Four basic logic functions:Four basic logic functions: NOTNOT

ANDAND

OR andOR and

Exclusive-OR.Exclusive-OR.


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The AND OperationThe AND Operation


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The AND OperationThe AND Operation


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The OR OperationThe OR Operation

Has two separate functions in a microprocessor-basedHas two separate functions in a microprocessor-based

system:system: It selectively sets bits of the accumulator orIt selectively sets bits of the accumulator or

Replaces discrete OR gates.Replaces discrete OR gates.

The inclusive-OR instruction functions as eightThe inclusive-OR instruction functions as eight

independent two-input OR gates.independent two-input OR gates.

This instruction replaces two 7432 two-input OR gates.This instruction replaces two 7432 two-input OR gates.


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Illustrative Program: ORing Data from Two InputIllustrative Program: ORing Data from Two Input


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PortsPorts

PROBLEM STATEMENTPROBLEM STATEMENT Two input port with eight switches (each port) at addressTwo input port with eight switches (each port) at address

00H and OIH (Figure 6.9) is connected to the00H and OIH (Figure 6.9) is connected to the

microcomputer to control the same appliances and lightsmicrocomputer to control the same appliances and lights

from the bedroom as well as from the kitchen.from the bedroom as well as from the kitchen.

Write instructions to turn on the devices from any of theWrite instructions to turn on the devices from any of the

input ports.input ports.

ll f


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PortsPorts



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PortsPorts

PROBLEM ANALYSISPROBLEM ANALYSIS To turn on the appliances from any one of the input ports, theTo turn on the appliances from any one of the input ports, the

microprocessor needs to read the switches at both ports and logicallymicroprocessor needs to read the switches at both ports and logically

OR the switch positions.OR the switch positions.

Assume that the switch positions in one input port (located in theAssume that the switch positions in one input port (located in thebedroom) correspond to the data byte 9lH and the switch positionsbedroom) correspond to the data byte 9lH and the switch positions

in the second port (located in the kitchen) correspond to the datain the second port (located in the kitchen) correspond to the data

byte A8H.byte A8H.

The person in the bedroom wants to turn on the air conditioner, theThe person in the bedroom wants to turn on the air conditioner, the

radio, and the bedroom light; and the person in the kitchen wants toradio, and the bedroom light; and the person in the kitchen wants toturn on the air-conditioner, the coffeepot, and the kitchen light.turn on the air-conditioner, the coffeepot, and the kitchen light.

By ORing these two data bytes, the MPU can turn ON the necessaryBy ORing these two data bytes, the MPU can turn ON the necessary

appliances.appliances.



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PortsPorts


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Exclusive OR (XOR)Exclusive OR (XOR)


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ROTATE INSTRUCTIONSROTATE INSTRUCTIONS


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SUMMARYSUMMARY

Most arithmetic and logic instructions affect the flag bits,whereas the data transfer instructions did not affect theflags.

Many arithmetic and logic instructions gate the result into

the accumulator.The arithmetic and logic instructions use register,

immediate, and register indirect addressing.

Addition is available as add 1 to any register or register pair,

8- and 16-bit binary, 8-bit binary with carry, and binary-coded decimal (BCD).


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SUMMARYSUMMARY

Subtraction is available as subtract 1 from any register orSubtraction is available as subtract 1 from any register orregister pair, 8-bit binary, 8-bit binary with borrow, and asregister pair, 8-bit binary, 8-bit binary with borrow, and as

a compare, which is a form of subtraction.a compare, which is a form of subtraction.

The logic operations are AND, OR, exclusive-OR, andThe logic operations are AND, OR, exclusive-OR, and

invert.invert.The logic instructions are ideal for control because ANDThe logic instructions are ideal for control because AND

clears bits, OR sets bits, and exclusive-OR complementsclears bits, OR sets bits, and exclusive-OR complements

bits. This gives the programmer complete control over eachbits. This gives the programmer complete control over each

bit of a number.bit of a number.Programmed logic replaces discrete logic circuits at aProgrammed logic replaces discrete logic circuits at a

substantial cost advantage.substantial cost advantage.


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SUMMARYSUMMARY

Some 8085 instructions have hidden functions: ADD Ashifts the accumulator left, and DAD H shifts HL left.

Both ANA A and ORA A test the accumulator, and SUB Aand XRA A clear the accumulator.

The rotate commands create the shift-right functions:logical and arithmetic shift right.


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P= 0 Odd parity


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Subtract with BorrowSubtract with Borrow


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Subtract with BorrowSubtract with Borrow


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ExampleExampleSuppose that the number in the DE pair must be subtracted fromthe BC pair. The least significant is operated on first. Once the

difference of C and E is found, the D register is subtracted fromthe B register with a borrow. The subtraction with borroweffectively propagates the borrow through the most significantbyte of the result.

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Instruction Set pec lecture