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16 BIT BARREL SHIFTER
HOLY MARY INSTITUTE OF TECHNOLOGY
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CONTENTS
BARREL SHIFTER CONTENTS
SARA
XXXX BARREL SHIFTER CHIP
SARA BLOCK DIAGRAM
VHDL CODING
SIMULATION
APPLICATIONS
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Barrel Shifter
Combinational logic circuit with n data inputs, n data
outputsand a set of control inputs
Control i/psspecify how to shift the data between input
andoutput
Part of pCPU that specifies the direction of shift(left or
right),type of shift and amount of shift from 0 to n-1 bits
Shift operation is controlled by 6 bits: Four bits for the
length,
one bit for direction, and one bit for type shift/rotate
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Contents
The 2 main blocks of barrel shifter are: shift-and-rotate array
(SARA) and the control logic
SARA performs the actual shift-and-rotate task onavailable data
while its controlling signals comesfrom control logic
SARA occupies most of the chip area, determinesthe critical path
delay of the barrel shifter and so
implemented in dynamic or D3L logic
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SARA
For a 16 bit barrel shifter, SARA is designed using 5stages each
with sixteen cells
Basic cell used in this array is an AO22 gate that iscalled
q-mux
Implements the function F= Ci1* In1 + Ci2* In2 ,where
Ci1,Ci2 come for control logic and
In1,In2 come from external inputs orprevious stage o/ps
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d3
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BARREL SHIFTER CHIP
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SARA BLOCK DIAGRAM
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SARA Implementation
Elimination of clk signal is done by substitution of
suitableinput combinations with external inputs (In1,In2) and
control
inputs (Ci1,Ci2)
Control logic o/psare set low in pre-charge phase to chargethe
entire circuit
When the condition In1=In2=0 is satisfied , each qmux cell
is
pre-charged and transition in In1 or In2 starts the
evaluationphase
Advantage over domino logic is conditional evaluation and
less power consumption
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Pre-charge by ext inputs
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Pre-charge by control inputs
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VHDL Coding
16 bit barrel shifter is implemented using behavioral model
through
modelsim
16 bit barrel shifter is implemented using behavioral model
through
modelsim
Types of operations performed here are 4 shift
operations(shr,shl,sar,sal) and 4 rotate
operations(ror,rol,rcl,rcr) that
are represented by opsel
Finally, We get 16 bit output after shift or rotate and an o/p
carry bit
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Simulations
For 2 bits shift or rotate:
Let, 16 bit input (a) = 1011001011000101;
4 bit control i/p (b)= 0010 ;opsel =000,010,100,110 ;
c_in= 0
Indicates the operations of logical shift left, arithmetic
shiftleft, rotate left and rotate carry left operations by 2
bitpositions
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Applications of barrel shifter
Digital Signal Processing
Array Processing
Graphics
Database Addressing
High Speed Arithmetic Processors
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THANKU
