This document discusses logic microoperations which specify binary operations for strings of bits stored in registers. It provides examples of selective set, selective complement, selective clear, mask, and insert operations. These logic microoperations are useful for manipulating individual bits or portions of words stored in registers. The document concludes with two assignment questions involving designing a circuit to perform logic operations on a two bit word and using logic microoperations to change the value stored in a register.

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Computer Organization
Instructors :
Dr. Abdul Raouf Khan
Mr.Marwan El-Haj
Logic Microoperations
Logic Microoperations specify binary
operations for strings of bits stored in
registers. Each bit is considered separately .
For example EX-OR operation is symbolized
by P : R1 R1 R2
it means, if P=1, EXOR operation of
individual bits of R1 and R2 are executed
and the result is placed in R1

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List of Logic Microoperations
Hardware implementation of
Logic Microoperations

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Applications
Logic Microoperations are very useful for
manipulating individual bits or portions of
word stored in a register.
1) Selective Set
The selective set operation sets to 1 the bits
in register A, where there are corresponding
1’s in register B
1 0 1 0 A (before)
1 1 0 0 B (logic operand)
-------------------
1 1 1 0 A ( after )
( Logic OR)

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2) Selective Complement
The selective Complement operation
complements bits in register A, where there
are corresponding 1’s in register B
1 0 1 0 A (before)
1 1 0 0 B (logic operand)
-------------------
0 1 1 0 A ( after )
( Logic XOR)
3) Selective Clear
The selective Clear operation clears to 0 the
bits in register A, only where there are
corresponding 1’s in register B
1 0 1 0 A (before)
1 1 0 0 B (logic operand)
-------------------
0 0 1 0 A ( after )
( Logic AB”)

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4) Mask operation
The bits in register A are cleared only
where there are corresponding 0’s in register
B
1 0 1 0 A (before)
1 1 0 0 B (logic operand)
-------------------
1 0 0 0 A ( after )
( Logic AND)
5) Insert operation
Inserts a new value into a group of bits
This is done by first masking the bits then
ORing them with the required value
0 1 1 0 1 0 1 0 A (before)
0 0 0 0 1 1 1 1 B (mask unwanted bits)
-------------------
0 0 0 0 1 0 1 0 A ( after masking)

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5) Insert operation (contd )
And Insert a new value
0 0 0 0 1 0 1 0 A ( after masking)
1 0 0 1 0 0 0 0 B (insert bits)
-------------------
1 0 0 1 1 0 1 0 A ( after insertion)
The clear operation compares the results
1 0 1 0 A
1 0 1 0 B
-------------------
0 0 0 0 A A B
Assignment
1. Design a digital circuit that performs the four logic
operations of EXOR, EXNOR, NOR and NAND. Use
two selection lines. Show the logic diagram of two
stages. ( for two bit word)
2. Register A holds the 8 – bit binary 11011001.
Determine the B operand and logic microoperation to
be performed in order to change the value in A to
a) 01101101
b) 11111101