The Logical Operations performed by ALU

1
The Logical Operations performed by ALU

• Bit Wise ANDing. (Binary).
• Bit Wise ORing (Binary).
• Bit Wise EX_ORing (Binary).
• Bit Wise NORing (Binary).
• Bit Wise NANDing (Binary).
• Bit Wise Inversion NOT (Unary).
• N.B In each of the above cases Zero flag
  Sign Flags only gets affected while Carry/Borrow
  Overflow Flags are preserved.

2
The Logical Operations Table

• BINARY OPERATIONS
• Sl. No. Operation O/P Logical Expression
  ALU Function Code
• 1. BIT Wise ANDing A .
  B
  0 1 0 0 0
• 2. BIT Wise ORing A
  B
  0 1 0 0 1
• 3. BIT Wise EXOR A ?
  B
  0 1 0 1 0
• 4. BIT Wise NOR A NOR
  B 0
  1 0 1 1
• 
  
• 5. BIT Wise NAND A NAND B
  0 1
  1 0 0
• 
  Inhibit affecting Cy OV Flags
• UNARY
  OPERATIONS ALU
  Function Code
• 6 BIT Wise Invert A NOT A
  0 1
  1 0 1
• 
  1110 1111 are
  forbidden
• _

3
The Logical Processing Section - 1

• Composed of the Following Blocks
• 1. A Group of n number of two (2) I/P AND
  Gates.
• 2. A Group of n number of two (2) I/P OR
  Gates.
• 3. A Group of n number of twp (2) I/P EX - OR
  Gates.
• 4. A Group of n number of two (2) I/P NAND
  Gates.
• 5. A Group of n number of two (2) I/P NOR
  Gates.
• 6. A Group of n number of NOT Gates.
• At the Logical Output part.
• a) A 6 to 1 , n bit, Group MUX with associated
  3 bit Selection.
• b) A selection bit (the MSB of OP Code) needed
  to Isolate ALL logical operations from the
  Arithmetic Group.

4
The Logical Processing Section - 2
N bits
N bits
N bits
N bits

N bits
N bits
N no of 2 I/P NAND
N no of 2 I/P NOR
N no of 2 I/P AND
N no of 2 I/P OR
N no of 2 I/P EX-OR
N no of NOT
N bits
N bits
N bits
N bits
N bits
S2
6 1 , n bit Group Mux
S1
S0
N bits LOGICAL O/P