The two’s complement adder-substractor can add or substract any two of the numbers in table 1. For exam-

ple :

Table 1 : Two’s Complement Numbers and Their Equivalent Decimal Values.

a) 2

SIGN

+ =

BIT

–5 X

0

0

000

01

0

2 +

Y

1

1

111

01

1

–5 +

CI

0

S 0 1

1

111

10

1 = –3

CO

TEST CIRCUITS

Quiescent Device Current.

Input Voltage.

Input Leakage Current.

SIGN

b) –2

BIT

– = X

1

111

11

1

0 –2 +

–5 Y

1

111

10

1

1 –5

Y

0

000

01

0

0

+

CL

1

S 1 0

000

00

1

1

= 3

CO

X8

X7

X6

X5

X4

X3

X2

X1

X8

X7

X6

X5

X4

X3

X2

X1

0

0

0

0

0

000=

0

111111

11=

-1

0

0

0

0

0

001=

1

111111

10=

-2

0

0

0

0

0

010=

2

111111

01=

-3

0

0

0

0

0

011=

3

111111

00=

-4

111110

11=

-5

0

1

1

1

1

110=

126

100000

01=

-127

0

1

1

1

1

111=

127

100000

00=

-128

HCC/HCF4030B

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