Chapter 6 Arithmetic Instructions and Programs

2002/4/82002/4/8 Microcomputers and MicroprocessorsMicrocomputers and Microprocessors 11

Suranaree UniversitySuranaree University

Of TechnologyOf Technologyมทสมทส

2002 Anant Oonsivilai2002 Anant Oonsivilai

Chapter 6Chapter 6Arithmetic Instructions Arithmetic Instructions

and Programsand Programs

222002/4/82002/4/8 Microcomputers and MicroprocessorsMicrocomputers and Microprocessors2002 Anant Oonsivilai2002 Anant Oonsivilai

OutlinesOutlines

Range of numbers in 8051 unsigned dataRange of numbers in 8051 unsigned dataAddition & subtraction instructions for unsigned Addition & subtraction instructions for unsigned datadataBCD system of data representationBCD system of data representationPacked and unpacked BCD dataPacked and unpacked BCD dataAddition & subtraction on BCD dataAddition & subtraction on BCD dataRange of numbers in 8051 signed dataRange of numbers in 8051 signed dataSigned data arithmetic instructionsSigned data arithmetic instructionsCarry & overflow problems & correctionsCarry & overflow problems & corrections


Addition of Unsigned NumbersAddition of Unsigned Numbers

ADDADD A, sourceA, source ; A = A + ; A = A + sourcesource


Addition of Individual BytesAddition of Individual Bytes


ADDC & Addition of 16-bit NumbersADDC & Addition of 16-bit Numbers

13C E73B 8D78 74

+


BCD Number SystemBCD Number System

Unpacked BCD: 1 byteUnpacked BCD: 1 byte

Packed BCD: 4 bitsPacked BCD: 4 bits


Adding BCD Numbers & DA InstructionAdding BCD Numbers & DA Instruction

MOVMOV A,#17HA,#17H

ADDADD A,#28HA,#28H

MOVMOV A,#47HA,#47H ;A=47H first BCD operand;A=47H first BCD operandMOVMOV B,#25HB,#25H ;B=25 second BCD operand;B=25 second BCD operand

ADDADD A,BA,B ;hex (binary) addition (A=6CH);hex (binary) addition (A=6CH)

DADA AA ;adjust for BCD addition(A=72H);adjust for BCD addition(A=72H)

HEXHEX BCDBCD

2929 0010 10010010 1001

++ 1818 +0001 1000 +0001 1000

4141 0100 00010100 0001 AC=1AC=1

++ 6 6 + 0110 + 0110

4747 0100 01110100 0111


ExampleExample


Subtraction of Unsigned NumbersSubtraction of Unsigned Numbers

SUBBSUBB A, sourceA, source ; A = A – source – CY; A = A – source – CY

SUBB when CY = 0SUBB when CY = 0 Take 2’s complement of subtracted (source)Take 2’s complement of subtracted (source) Add it to minuendAdd it to minuend Invert carryInvert carry


Example (Positive Result)Example (Positive Result)


Example (Negative Result)Example (Negative Result)


SUBB When CY = 1SUBB When CY = 1For multibyte numbersFor multibyte numbers


Multiplication of Unsigned NumbersMultiplication of Unsigned Numbers

MULMUL ABAB ; A ; A B, place 16-bit result in B and A B, place 16-bit result in B and A

MOVMOV A,#25HA,#25H ;load 25H to reg. A;load 25H to reg. A

MOVMOV B,#65HB,#65H ;load 65H in reg. B;load 65H in reg. B

MULMUL ABAB ;25H * 65H = E99 where;25H * 65H = E99 where

;B = 0EH and A = 99H;B = 0EH and A = 99H

Table 6-1:Unsigned Multiplication Summary (MUL AB)Table 6-1:Unsigned Multiplication Summary (MUL AB)

MultiplicationMultiplication Operand 1Operand 1 Operand 2Operand 2 ResultResult

byte byte bytebyte AA BB A=low byte,A=low byte,

B=high byteB=high byte


Division of Unsigned NumbersDivision of Unsigned Numbers

DIVDIV ABAB ; divide A by B; divide A by B

MOVMOV A,#95HA,#95H ;load 95 into A;load 95 into A

MOVMOV B,#10HB,#10H ;load 10 into B;load 10 into B

DIVDIV ABAB ;now A = 09 (quotient) and ;now A = 09 (quotient) and

;B = 05 (remainder);B = 05 (remainder)

Table 6-2:Unsigned Division Summary (DIV AB)Table 6-2:Unsigned Division Summary (DIV AB)

DivisionDivision NumeratorNumerator DenominatorDenominator QuotientQuotient RemainderRemainder

byte / bytebyte / byte AA BB AA BB


Example ( 1 of 2 )Example ( 1 of 2 )


Example ( 2 of 2 )Example ( 2 of 2 )


Signed 8-bit OperandsSigned 8-bit Operands

Covert to 2’s complementCovert to 2’s complement Write magnitude of number in 8-bit binary (no Write magnitude of number in 8-bit binary (no

sign)sign) Invert each bitInvert each bit Add 1 to itAdd 1 to it


ExampleExample


Byte-sized Signed Numbers Byte-sized Signed Numbers RangesRanges

DecimalDecimal BinaryBinary HexHex

-128-128 1000 00001000 0000 8080

-127-127 1000 00011000 0001 8181

-126-126 1000 00101000 0010 8282

…….. …………………… ....

-2-2 1111 11101111 1110 FEFE

-1-1 1111 11111111 1111 FFFF

00 0000 00000000 0000 0000

+1+1 0000 00010000 0001 0101

+2+2 0000 00100000 0010 0202

…… …………………… ......

+127+127 0111 11110111 1111 7F7F


Overflow in Signed Number Overflow in Signed Number OperationsOperations


When Is the OV Flag Set?When Is the OV Flag Set?

Either: there is a carry from D6 to D7 but Either: there is a carry from D6 to D7 but no carry out of D7 (CY = 0)no carry out of D7 (CY = 0)

Or: there is a carry from D7 out (CY = 1) Or: there is a carry from D7 out (CY = 1) but no carry from D6 to D7but no carry from D6 to D7


ExampleExample

Chapter 6 Arithmetic Instructions and Programs

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