Shift microoperations are used to serially transfer data and are used with arithmetic, logical, and other data processing units. There are three types of shifts: 1) logical shifts transfer zeros into the shifted bits, 2) circular shifts circulate bits around the two ends of the register, and 3) arithmetic shifts preserve the sign bit during a right shift and insert zeros during a left shift, changing the sign if overflow occurs. The document discusses drawing logic circuits to perform six shift microoperations on a 4-bit register and includes bonus points for detecting overflow.

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Computer Organization
Instructors :
Dr. Abdul Raouf Khan
Mr.Marwan El-Haj
Shift Microoperations
Shift Microoperations are used for serial transfer of
data. They are also used with arithmetic, logical and
other data processing units. The contents of a
register can be shifted to the left or right, with the flip
Flops receiving data from serial inputs.

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Types of Shift Microoperations
There are three types of Shifts
1) Logical shift
2) Circular shift
3) Arithmetic shift
1. Logical shift
A logical Shift transfers ‘0’ through the serial
input and bits are shifted one bit to the left or
right. A logical shift (shl) transfers ‘0’ in bit
position R0 and right shift (shr) transfers ‘0’
in bit position Rn-1.

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2. circular shift
A circular Shift (also called a rotate operation)
circulates the bits of the register around the
two ends. The serial output is connected to the
serial input. The shift can be left (cil) or right
(cir).
3. Arithmetic shift
An arithmetic shift, shifts a signed binary number to
the left or right.
The arithmetic shift right (ashr) leaves the sign bit
unchanged and shifts the number (including the sign
bit) to the right. Rn-1 remains the same. R0 is lost
The arithmetic shift left (ashl) inserts a ‘0’ into R0 and
shifts all other bits to the left. A sign change takes
place if Rn-1 changes value, this is due to overflow ( if
Rn-1 Rn-2=1)

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Assignment 4
Draw the logic circuit for the 6 shift Micro
operations Considering Register A Size of 4
bits.
Bonus Point will be given for the student who
add the part of overflow detection(either
before or after occuring)
Bidirectional shift register with parallel load

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Bidirectional shift register with parallel load
4-Bit Combinational Circuit Shifter
Function Table
Select Output
S H3 H2 H1 H0
0 A2 A1 A0 IR
1 IL A3 A2 A1

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Arithmetic Logical Shift Unit