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TK 2633: Microprocessor & Interfacing. Lecture 5: Arithmetic and Logic Instructions. OBJECTIVES. Explain the operation of the 8085 arithmetic and logic instructions and describe their effect on the flag bits. Describe how DAA adjusts the result of a BCD addition.

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Tk 2633 microprocessor interfacing

TK 2633:Microprocessor & Interfacing

Lecture 5: Arithmetic and Logic Instructions


Objectives
OBJECTIVES

  • Explain the operation of the 8085 arithmetic and logic instructions and describe their effect on the flag bits.

  • Describe how DAA adjusts the result of a BCD addition.

  • Write short programs using the arithmetic and logic operations.

  • Use the logic instructions to clear, set, and complement bus.

  • Test the accumulator, using the ANA A or ORA A instruction.

  • Explain the operation of the shift and rotate instructions and their effect on the flag bits.

Prepared by: Dr Masri Ayob - TK2123


Arithmetic operations
ARITHMETIC OPERATIONS

  • Addition,

  • subtraction,

  • increment,

  • and decrement.

Prepared by: Dr Masri Ayob - TK2123


Arithmetic operations1
ARITHMETIC OPERATIONS

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Arithmetic operations2
ARITHMETIC OPERATIONS

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Arithmetic operations3
ARITHMETIC OPERATIONS

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Arithmetic operations4
ARITHMETIC OPERATIONS

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Addition
ADDITION

  • Addition takes several forms in the 8085 microprocessor:

    • 8-bit binary,

    • 16-bit binary,

    • and two-digit binary-coded-decimal (BCE)) addition.

  • Binary addition functions with either signed or unsigned numbers;

  • BCD addition uses only unsigned numbers.

  • The instruction set supports additions using register addressing, register indirect addressing, and immediate addressing, but not direct addressing.

Prepared by: Dr Masri Ayob - TK2123


Addition1
ADDITION

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Addition2
ADDITION

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Addition3
ADDITION

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Addition with carry
Addition with Carry

  • Whenever large numbers (numbers wider than 8 bits, or multiple-byte numbers) are added, the carry must be propagated from one 8-bit segment to the next.

Prepared by: Dr Masri Ayob - TK2123


Addition with carry1
Addition with Carry

Prepared by: Dr Masri Ayob - TK2123


Example
Example

  • Suppose that the DE register pair contains a 16-bit number that we must add to the number in the BC register pair. To accomplish this multiple-byte addition, add F and C together and then add D and B together with the carry. The add-with-carry instruction uses the carry from the addition of E and C to generate the correct answer when D and B are added.

Prepared by: Dr Masri Ayob - TK2123


Example1
Example

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Sixteen bit addition
Sixteen-Bit Addition

  • The 8085 instruction set does contain special instructions (DAD) that do 16-bit addition.

Prepared by: Dr Masri Ayob - TK2123


Bcd addition
BCD Addition

  • BCD addition is like binary addition except that the numbers range in value only from 0 through 9.

  • A special instruction allows BCD addition by using the standard binary addition (ADD) instructions.

    • The DAA instruction appears after a BCD addition (with a binary add instruction) to correct the BCD result.

    • The DAA instruction does not convert a binary number to a BCD number.

Prepared by: Dr Masri Ayob - TK2123


Example2
Example

  • Example 5-6 illustrates the summation of the packed BCD numbers 11 and 19.

  • After this addition, the accumulator contains a 2AH, which is not a BCD number:

    • the answer should be a 30BCD

    • The DAA instruction corrects the answer after the addition and provides a 30BCD after the DAA instruction executes.

Prepared by: Dr Masri Ayob - TK2123


Bcd addition1
BCD Addition

  • The DAA instruction changes the result through the two tests listed by adding a OOH, 06H, 60H, or 66H to the accumulator.

    • If the least significant half-byte is greater than 9 or if the AC flag = 1, the DAA instruction adds a 06H to the accumulator.

    • If the most significant half-byte is greater than 9 or if the C flag bit 1, the DAA instruction adds a 60H to the accumulator.

Prepared by: Dr Masri Ayob - TK2123


Increment
Increment

  • The last form of addition is to increment or add 1.

  • The increment command is either an 8-bit (INR) increment or a 16-bit (INX) Increment instruction.

  • The INR instructions affect all the flags except carry, and the INX instructions affect no flags.

Prepared by: Dr Masri Ayob - TK2123



Subtraction
Subtraction

  • The 8085 supports 8-bit binary subtraction and decrement.

  • It also supports a subtraction instruction that allows a borrow to be propagated through additional bytes of a number.

  • The subtract-with-borrow instruction aids in the subtraction of multiple-byte numbers. .

Prepared by: Dr Masri Ayob - TK2123


Subtraction1
Subtraction

  • The 8085 performs subtraction by using the method of 2’s 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).

Prepared by: Dr Masri Ayob - TK2123


Subtraction2
Subtraction

  • Various subtraction instructions: register, register indirect, and immediate addressing.

  • Direct addressing is not allowed for a subtraction.

  • Each of these instructions affects the flag bits, so they reflect various conditions about the difference after a subtraction.

Prepared by: Dr Masri Ayob - TK2123


Subtraction3
Subtraction

  • The 8085 performs the following steps internally to execute the instruction SUB (or SUI):

    • Converts subtrahend (the number to be subtracted) into its 1’s complement.

    • Adds 1I to 1’s complement to obtain 2’s complement of the subtrahend.

    • Add 2’s complement to the minuend (the contents of the accumulator).

    • Complements the Carry flag.

Prepared by: Dr Masri Ayob - TK2123


Illustrative program subtraction of two numbers
Illustrative Program: Subtraction of Two Numbers

  • PROBLEM STATEMENT

    • Write a program to do the following:

      • Load the number 3011 in register B and 3911 in register C.

      • Subtract 39H from 3011.

      • Display the answer at PORT I.

Prepared by: Dr Masri Ayob - TK2123


Illustrative program subtraction of two numbers1
Illustrative Program: Subtraction of Two Numbers

Prepared by: Dr Masri Ayob - TK2123


Illustrative program subtraction of two numbers2
Illustrative Program: Subtraction of Two Numbers

  • PROGRAM DESCRIPTION

    • Registers B and C are loaded with 30H and 39H, respectively.

    • The instruction MOV A,B copies 30H into the accumulator (shown as register contents).

Prepared by: Dr Masri Ayob - TK2123


Illustrative program subtraction of two numbers3
Illustrative Program: Subtraction of Two Numbers

  • To execute the instruction SUB C the microprocessor performs the following steps internally:

Prepared by: Dr Masri Ayob - TK2123


Illustrative program subtraction of two numbers4
Illustrative Program: Subtraction of Two Numbers

  • PROGRAM DESCRIPTION

    • The number F7H is a 2’s complement of the magnitude (39H-30H)=09H.

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

    • The instruction OUT displays F7 at PORT1.

Prepared by: Dr Masri Ayob - TK2123


Subtraction4
Subtraction

P= 0 Odd parity

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Subtract with borrow
Subtract with Borrow

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Subtract with borrow1
Subtract with Borrow

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Example3
Example

Suppose that the number in the DE pair must be subtracted from the BC pair. The least significant is operated on first. Once the difference of C and E is found, the D register is subtracted from the B register with a borrow. The subtraction with borrow effectively propagates the borrow through the most significant byte of the result.

Prepared by: Dr Masri Ayob - TK2123


Logic instructions
LOGIC INSTRUCTIONS

  • Four basic logic functions:

    • invert, AND, OR, and exclusive-OR.

  • Why does a microprocessor instruction set contain logic instructions?

    • Logic instructions sometimes replace discrete logic gates.

    • Today, program storage costs about of a cent per byte.

    • System control software usually requires bit manipulation — a logic operation.

Prepared by: Dr Masri Ayob - TK2123


Inversion not
Inversion (NOT)

  • The CMA instruction (2FH in machine language), one’s-complements or inverts the contents of the accumulator.

  • This operation, which affects none of the flag bits, causes each bit of the accumulator to be inverted (changed from 1 to 0 or 0 to 1).

  • The CMA instruction causes the accumulator to appear as eight inverters (or NOT).

    • This means that this one-byte instruction replaces eight discrete inverters if the speed required is not too great. The amount of circuitry replaced by the CMA instruction is 14 of a 7404 TTL hex inverter.

Prepared by: Dr Masri Ayob - TK2123


The and operation
The AND Operation

  • The AND instruction, has two separate functions in a microprocessor-based system.

    • The AND instruction selectively clears bits of the accumulator or replaces discrete AND gates.

  • The AND instruction, functions as eight independent two-input AND gates. This instruction replaces two 7408 quad two-input AND gates.

Prepared by: Dr Masri Ayob - TK2123


The and operation1
The AND Operation

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The and operation2
The AND Operation

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The or operation
The OR Operation

  • Has two separate functions in a microprocessor-based system:

    • It selectively sets bits of the accumulator or

    • Replaces discrete OR gates.

  • The inclusive-OR instruction functions as eight independent two-input OR gates.

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

Prepared by: Dr Masri Ayob - TK2123


The or operation1
The OR Operation

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The or operation2
The OR Operation

Prepared by: Dr Masri Ayob - TK2123



Illustrative program oring data from two input ports
Illustrative Program: ORing Data from Two Input Ports

  • PROBLEM STATEMENT

    • Two input port with eight switches (each port) at address 00H and OIH (Figure 6.9) is connected to the microcomputer to control the same appliances and lights from the bedroom as well as from the kitchen.

    • Write instructions to turn on the devices from any of the input ports.

Prepared by: Dr Masri Ayob - TK2123


Illustrative program oring data from two input ports1
Illustrative Program: ORing Data from Two Input Ports

Prepared by: Dr Masri Ayob - TK2123


Illustrative program oring data from two input ports2
Illustrative Program: ORing Data from Two Input Ports

  • PROBLEM ANALYSIS

    • To turn on the appliances from any one of the input ports, the microprocessor needs to read the switches at both ports and logically OR the switch positions.

    • Assume that the switch positions in one input port (located in the bedroom) correspond to the data byte 9lH and the switch positions in the second port (located in the kitchen) correspond to the data byte A8H.

    • The person in the bedroom wants to turn on the air conditioner, the radio, and the bedroom light; and the person in the kitchen wants to turn on the air-conditioner, the coffeepot, and the kitchen light.

    • By ORing these two data bytes, the MPU can turn ON the necessary appliances.

Prepared by: Dr Masri Ayob - TK2123


Illustrative program oring data from two input ports3
Illustrative Program: ORing Data from Two Input Ports

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Exclusive or xor
Exclusive OR (XOR)

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Rotate instructions
ROTATE INSTRUCTIONS

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Shift instructions
SHIFT INSTRUCTIONS

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Summary
SUMMARY

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

  • 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).

Prepared by: Dr Masri Ayob - TK2123


Summary1
SUMMARY

  • Subtraction is available as subtract 1 from any register or register pair, 8-bit binary, 8-bit binary with borrow, and as a compare, which is a form of subtraction.

  • The logic operations are AND, OR, exclusive-OR, and invert.

  • The logic instructions are ideal for control because AND clears bits, OR sets bits, and exclusive-OR complements bits. This gives the programmer complete control over each bit of a number.

  • Programmed logic replaces discrete logic circuits at a substantial cost advantage.

Prepared by: Dr Masri Ayob - TK2123


Summary2
SUMMARY

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

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

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

Prepared by: Dr Masri Ayob - TK2123


Thank you q a
Thank youQ&A

Prepared by: Dr Masri Ayob - TK2123


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