Functional Units for Addition and Subtraction Functional Units for Addition and Subtraction Functional Units for Addition and Subtraction Functional Units for Addition and Subtraction Functional Units for Addition and Subtraction Functional Units for Addition and Subtraction Functional Units for Addition and Subtraction Functional Units for Addition and Subtraction Carry LookAhead Adder 10.2.2 Carry LookAhead Adder
Trang 110.2 Functional Units for Addition and Subtraction
10.2.1 Ripple Carry Adder
S= a b⊕ b Cout = a & b Half adder
Trang 210.2 Functional Units for Addition and Subtraction
10.2.2 Carry Look-Ahead Adder
• Arithmetic implementation of carry bit
generate: gi = ai & bi
propagate: pi = ai ^ bi
si = (ai ^ bi) ^ci = pi^ci
Ci +1 = (( ai ^ bi ) & ci ) | ( a & b ) = ( pi & ci )^gi
Trang 310.2 Functional Units for Addition and Subtraction
10.2.2 Carry Look-Ahead Adder
• 4 bit Arithmetic implementation of carry
bit
Ci +1 = (( ai ^ bi ) & ci ) | ( a & b ) = ( pi & ci )^gi
Trang 410.2 Functional Units for Addition and Subtraction
10.2.2 Carry Look-Ahead Adder
• 4-bit adder with carry look ahead
Trang 510.2 Implementation 4-bit adder with carry look ahead
10.2.2 Carry Look-Ahead Adder
Trang 610.2 Functional Units for Addition and Subtraction
10.2.3 Overflow and Underflow
Positive + positive = negative y
Negative + negative = positive
=> include logic for Overflow and
Underflow detection