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State University of New York at Stony Brook
Department of Electrical and Computer Engineering
ESE 218 Digital Systems Design
Spring 2009
Lab
4.
Code Converter
1. Objectives
Your task is to design a threebit
BinarytoEx3
converter
.
It was reduced to three bits
for circuit simplicity. Excess3 code
is obtained
from the binary one by addition of 3.
The block diagram is shown in Figure 1. The binary code is applied to the
combinational circuit inputs I
0
, I
1
and I
2
and the circuit produces output
functions
O
0
, O
1
and
O
2
in accordance with
the
truth
table
Figure 1.
Binary
Excess3
Decimal
code
I
2
I
1
I
0
O
2
O
1
O
0
0
0
0
0
0
1
1
1
0
0
1
1
0
0
2
0
1
0
1
0
1
3
0
1
1
1
1
0
4
1
0
0
1
1
1
5
1
0
1
0
0
0
6
1
1
0
0
0
1
7
1
1
1
0
1
0
Excess3 code is an example of selfcomplementing codes. Such codes have the property
that the 9’s complement of a decimal number is obtained directly by changing 1’s to 0’s
and 0’s to 1’s in this code (verify it for decimal codes 2 and 7, 3 and 6, 4 and 5).
Although the truth table representation of a function is unique, the implementation can
appear in many different forms.
In the prelab you can practice with algebraic manipulations
to obtain the implementation with a minimal number of 74LS chips (see the text below).
I
0
I
1
I
2
O
0
O
1
O
2
Binary code
Excess3 code
Logic gates
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2. Preliminary lab
1. Logic maps
The output functions can be simplified by
various
methods
including al
gebraic manipulation,
Kmap or by means of
algorithmic methods
.
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This note was uploaded on 04/12/2009 for the course ESE 218 taught by Professor Donetsky during the Spring '08 term at SUNY Stony Brook.
 Spring '08
 DONETSKY

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