Functional Units for Addition and Subtraction
Bạn đang xem bản rút gọn của tài liệu. Xem và tải ngay bản đầy đủ của tài liệu tại đây (227.32 KB, 6 trang )
10.2 Functional Units for Addition and Subtraction
10.2.1 Ripple Carry Adder
Half adder
S= a ⊕ b
Cout = a & b
10.2 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
10.2 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
10.2 Functional Units for Addition and Subtraction
10.2.2 Carry Look-Ahead Adder
• 4-bit adder with carry look ahead
10.2 Implementation 4-bit adder with carry look ahead
10.2.2 Carry Look-Ahead Adder
10.2 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
