Binary Adder-Subtractor



Rating - 3/5
547 views

The subtraction of binary numbers can be done most conveniently by means of complements as discussed in Sec. 3-2. Remember that the subtraction A - B can be done by taking the 2's complement of B and adding it to A. The 2's complement can be obtained by taking the 1' s complement and adding one to the least significant pair of bits. The 1's complement can be implemented with inverters and a one can be added to the sum through the input carry.

 

 

 

These Topics Are Also In Your Syllabus
1 Three-State Bus Buffers link
2 Memory Transfer link
You May Find Something Very Interesting Here. link
3 Binary Adder link
4 Binary Adder-Subtractor link
5 Binary lncrementer link

 

 

 

 

 

These Topics Are Also In Your Syllabus
1 Input-Output and Interrupt link
2 Input - output Register link
You May Find Something Very Interesting Here. link
3 Complete Computer Description link
4 Design of Basic Computer link
5 Types Of Systems link

 

 

The addition and subtraction operations can be combined into one common circuit by including an exclusive-OR gate with each full-adder. A 4-bit adder-subtractor circuit is shown in Fig. 4-7. The mode input M controls the operation. When M = 0 the circuit is an adder and when M = 1 the circuit becomes a subtractor. Each exclusive-OR gate receives input M and one of the inputs of B. When M = 0, we have B a1 0 = B. The full-adders receive the value of B, the input carry is O, and the circuit performs A plus B. When M = 1, we have B a1 1 = B' and C0 = 1. The B inputs are all complemented and a 1 is added through the input carry. The circuit performs the operation A plus the 2's complement of B. For unsigned numbers, this gives A - B if A '" B or the 2's complement of (8 - A) if A < B. For signed numbers, the result is A - B provided that there Is no overflow.


Rating - 3/5
468 views

Advertisements
Rating - 3/5