The document describes implementing an alphanumeric display using a seven-segment display on the Nexys 4 DDR FPGA kit by applying binary inputs through switches to show numbers (0-9) and letters (a-z). The project employs VHDL programming to decode ASCII values into corresponding outputs on the display. It outlines the use of both common anode and common cathode types of seven-segment displays and details the code logic for displaying numerals and letters.

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IMPLEMENTATION OF ALPHANUMERIC ON A SEVEN
SEGMENT DISPLAY
OBJECTIVE
The main idea behind this is to implement the BINARY INPUT TO DISPLAY LETTERS AND
NUMBERS ON A SEVEN SEGMENT DISPLAY available on the NEXYS 4 DDR. In this the
binary input is applied through switches available on the board and the output will be a
combinational display of number’s (0-9) and letters from (a to z).
Tools:
Software Tools– Xilinx VIVADO design suite 14.2
Hardware Tools – Nexys 4 DDR
Basic idea:
Generally the seven segment displays are used in digital circuits to represent numbers. One of the
most common applications is in digital watches. We can implement the seven segment display
using BCD/HEXA input in which all the numbers from 0 to 9 are displayed and a letters from a
to f can be implemented, but using the single input values/ ASCII values (in binary format) as
inputs we wanted to generate all the letters from a to z and numbers from 0 to 9 on a single
platform.
The general idea representation is as shown below:
Letter ASCII Code Binary Letter ASCII Code Binary
a 097 01100001 A 065 01000001
b 098 01100010 B 066 01000010
c 099 01100011 C 067 01000011
Here we use the switches available on the Nexys board to provide the binary bits as input. The
binary input corresponding to the ASCII value has a letter associate with it which is displayed on
the seven segments corresponding to the VHDL program.
An example representation of the visual idea of the project described:

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Block diagram
Fig.1 Block Diagram for Alpha Numeric on Seven Segment.
Seven Segment Display
A seven segment display is a form of electronic display device which is used to display
numerals. We can commonly find the seven segment display in digital devices which is used to
represent the numeric information to user, like watches, calculators, electronic instruments etc.
The name seven segment display itself states that it is a combination of seven segments of
display which are arranged in a fashion to represent numerals, when programmed in different
fashion. These seven different segments are marked from A-G as in, fig (2).
Fig 2: A Generalized Seven Segment Display.
FPGA Hardware Kit
6 5 4 3 2 1 0
Switches
s
Input
ASCII
Code
Simulation
& Synthesis
in Vivado
14.2
Simulated
Waveform
Seven segment array
Output Seven
Segment
Display

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Types of seven segment display:
There are two types of seven segment display namely
1) Common Anode 7-segment display
2) Common Cathode 7-segment display
Display of Numerals &Letters
All the numerals can be displayed on the seven segment display. Along with the displaying of
numerals we can also display all the alphabets on the seven segments. A series of seven
segments display can also be used to represent words and scrolling sentences. The different
display of letters can be seen in the fig (2).
Fig 2: Seven segment display of letters and numerals
The project gives a basic idea of how the seven segment display is used to implement the display
of numerals and letters using 8 bits of binary input, using the NEXYS 4 DDR FPGA kit.
We have used VHDL coding to program the FPGA [XC100tcsg1] so that the binary input given
through switches is decoded according to the program which consists of defined modules to
convert the binary input to corresponding seven segment output. According to the program
output the seven segments glow to represent the corresponding output.

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In the project we have used a common anode type Seven segment display, hence to make a
segment ‘ON’ we have to provide logic ‘0’ and to make a segment ‘OFF’ we have to provide
logic ‘1’.
Binary Switch Logic
INPUTS
Fig.3 Segment and switch number representation
1 1 1 1 1 1 1
0 0 0 0 0 0 0
SWITCH
ON
SWITCH
OFF
sw1 sw2 sw3 sw4 sw5 sw6 sw7

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Aim:
To program the FPGA [XC100tcsg1] in VHDL for display numerals and letters on the seven
segments by providing 8 bit binary as input and to verify the output using the hardware kit.
Apparatus:
Hardware: Nexys 4 DDR FPGA kit.
Software: Xilinx Vivado design suite 14.2.
Verilog code:
module binary_to_seven_segment_display_project(
input [6:0] ip,
output a,b,c,d,e,f,g,
output [7:0] an
);
reg a,b,c,d,e,f,g;
reg [7:0] an = 8'b11111110;
always @ (ip) // checks for every change in input
// Code for Alphabets
if(ip[5] && ip[6])
begin
if(ip[0] && ~ip[1] && ~ip[2] && ~ip[3] && ~ip[4])
begin: a1
a=1'b0; b=1'b0; c=1'b0; d=1'b0; e=1'b0; f=1'b1; g=1'b0;
end
else if(~ip[0] &&ip[1] && ~ip[2] && ~ip[3] && ~ip[4])
begin : b1
a=1'b1; b=1'b1; c=1'b0; d=1'b0; e=1'b0; f=1'b0; g=1'b0;
end
else if(ip[0] &&ip[1] && ~ip[2] && ~ip[3] && ~ip[4])
begin: c1
a=1'b1; b=1'b1; c=1'b1; d=1'b0; e=1'b0; f=1'b1; g=1'b0;
end
else if(~ip[0] && ~ip[1] &&ip[2] && ~ip[3] && ~ip[4])
begin: d1
a=1'b1; b=1'b0; c=1'b0; d=1'b0; e=1'b0; f=1'b1; g=1'b0;
end

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else if(ip[0] && ~ip[1] &&ip[2] && ~ip[3] && ~ip[4])
begin: e1
a=1'b0; b=1'b0; c=1'b1; d=1'b0; e=1'b0; f=1'b0; g=1'b0;
end
else if(~ip[0] &&ip[1] &&ip[2] && ~ip[3] && ~ip[4])
begin: f1
a=1'b0; b=1'b1; c=1'b1; d=1'b1; e=1'b0; f=1'b0; g=1'b0;
end
else if(ip[0] &&ip[1] &&ip[2] && ~ip[3] && ~ip[4])
begin: g1
a=1'b0; b=1'b0; c=1'b0; d=1'b0; e=1'b1; f=1'b0; g=1'b0;
end
else if(~ip[0] && ~ip[1] && ~ip[2] &&ip[3] && ~ip[4])
begin: h
a=1'b1; b=1'b1; c=1'b0; d=1'b1; e=1'b0; f=1'b0; g=1'b0;
end
else if(ip[0] && ~ip[1] && ~ip[2] &&ip[3] && ~ip[4])
begin: i
a=1'b1; b=1'b1; c=1'b1; d=1'b1; e=1'b0; f=1'b0; g=1'b1;
end
else if(~ip[0] &&ip[1] && ~ip[2] &&ip[3] && ~ip[4])
begin: j
a=1'b1; b=1'b0; c=1'b0; d=1'b0; e=1'b0; f=1'b1; g=1'b1;
end
else if(ip[0] &&ip[1] && ~ip[2] &&ip[3] && ~ip[4])
begin: k
a=1'b1; b=1'b0; c=1'b0; d=1'b1; e=1'b0; f=1'b0; g=1'b0;
end
else if(~ip[0] && ~ip[1] &&ip[2] &&ip[3] && ~ip[4])
begin: l
a=1'b1; b=1'b0; c=1'b0; d=1'b1; e=1'b1; f=1'b1; g=1'b1;
end
else if(ip[0] && ~ip[1] &&ip[2] &&ip[3] && ~ip[4])
begin: m
a=1'b0; b=1'b1; c=1'b0; d=1'b1; e=1'b0; f=1'b1; g=1'b1;
end
else if(~ip[0] &&ip[1] &&ip[2] &&ip[3] && ~ip[4])
begin: n
a=1'b1; b=1'b1; c=1'b0; d=1'b1; e=1'b0; f=1'b1; g=1'b0;
end
else if(ip[0] &&ip[1] &&ip[2] &&ip[3] && ~ip[4])
begin: o
a=1'b1; b=1'b1; c=1'b0; d=1'b0; e=1'b0; f=1'b1; g=1'b0;
end
else if(~ip[0] && ~ip[1] && ~ip[2] && ~ip[3] &&ip[4])
begin: p

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a=1'b0; b=1'b0; c=1'b1; d=1'b1; e=1'b0; f=1'b0; g=1'b0;
end
else if(ip[0] && ~ip[1] && ~ip[2] && ~ip[3] &&ip[4])
begin: q
a=1'b0; b=1'b0; c=1'b0; d=1'b1; e=1'b1; f=1'b0; g=1'b0;
end
else if(~ip[0] &&ip[1] && ~ip[2] && ~ip[3] &&ip[4])
begin: r
a=1'b1; b=1'b1; c=1'b1; d=1'b1; e=1'b0; f=1'b1; g=1'b0;
end
else if(ip[0] &&ip[1] && ~ip[2] && ~ip[3] &&ip[4])
begin: s
a=1'b0; b=1'b1; c=1'b0; d=1'b0; e=1'b1; f=1'b0; g=1'b0;
end
else if(~ip[0] && ~ip[1] &&ip[2] && ~ip[3] &&ip[4])
begin: t
a=1'b1; b=1'b1; c=1'b1; d=1'b0; e=1'b0; f=1'b0; g=1'b0;
end
else if(ip[0] && ~ip[1] &&ip[2] && ~ip[3] &&ip[4])
begin: u
a=1'b1; b=1'b1; c=1'b0; d=1'b0; e=1'b0; f=1'b1; g=1'b1;
end
else if(~ip[0] &&ip[1] &&ip[2] && ~ip[3] &&ip[4])
begin: v
a=1'b1; b=1'b0; c=1'b0; d=1'b0; e=1'b0; f=1'b0; g=1'b1;
end
else if(ip[0] &&ip[1] &&ip[2] && ~ip[3] &&ip[4])
begin: w
a=1'b1; b=1'b0; c=1'b1; d=1'b0; e=1'b1; f=1'b0; g=1'b1;
end
else if(~ip[0] && ~ip[1] && ~ip[2] &&ip[3] &&ip[4])
begin: x
a=1'b1; b=1'b0; c=1'b0; d=1'b1; e=1'b0; f=1'b0; g=1'b0;
end
else if(ip[0] && ~ip[1] && ~ip[2] &&ip[3] &&ip[4])
begin: y
a=1'b1; b=1'b0; c=1'b0; d=1'b0; e=1'b1; f=1'b0; g=1'b0;
end
else if(~ip[0] &&ip[1] && ~ip[2] &&ip[3] &&ip[4])
begin: z
a=1'b0; b=1'b0; c=1'b1; d=1'b0; e=1'b0; f=1'b1; g=1'b0;
end
end
else

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begin: numbers
if(~ip[5] && ~ip[6])
// Code for Numbers
begin
if(~ip[0] && ~ip[1] && ~ip[2] && ~ip[3] && ~ip[4])
begin: zero
a=1'b0; b=1'b0; c=1'b0; d=1'b0; e=1'b0; f=1'b0; g=1'b1;
end
else if(ip[0] && ~ip[1] && ~ip[2] && ~ip[3] && ~ip[4])
begin: one
a=1'b1; b=1'b0; c=1'b0; d=1'b1; e=1'b1; f=1'b1; g=1'b1;
end
else if(~ip[0] &&ip[1] && ~ip[2] && ~ip[3] && ~ip[4])
begin: two
a=1'b0; b=1'b0; c=1'b1; d=1'b0; e=1'b0; f=1'b1; g=1'b0;
end
else if(ip[0] &&ip[1] && ~ip[2] && ~ip[3] && ~ip[4])
begin: three
a=1'b0; b=1'b0; c=1'b0; d=1'b0; e=1'b1; f=1'b1; g=1'b0;
end
else if(~ip[0] && ~ip[1] &&ip[2] && ~ip[3] && ~ip[4])
begin: four
a=1'b1; b=1'b0; c=1'b0; d=1'b1; e=1'b1; f=1'b0; g=1'b0;
end
else if(ip[0] && ~ip[1] &&ip[2] && ~ip[3] && ~ip[4])
begin: five
a=1'b0; b=1'b1; c=1'b0; d=1'b0; e=1'b1; f=1'b0; g=1'b0;
end
else if(~ip[0] &&ip[1] &&ip[2] && ~ip[3] && ~ip[4])
begin: six
a=1'b0; b=1'b1; c=1'b0; d=1'b0; e=1'b0; f=1'b0; g=1'b0;
end
else if(ip[0] &&ip[1] &&ip[2] && ~ip[3] && ~ip[4])
begin: seven
a=1'b0; b=1'b0; c=1'b0; d=1'b1; e=1'b1; f=1'b1; g=1'b1;
end
else if(~ip[0] && ~ip[1] && ~ip[2] &&ip[3] && ~ip[4])
begin: eight
a=1'b0; b=1'b0; c=1'b0; d=1'b0; e=1'b0; f=1'b0; g=1'b0;
end
else if(ip[0] && ~ip[1] && ~ip[2] &&ip[3] && ~ip[4])

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begin: nine
a=1'b0; b=1'b0; c=1'b0; d=1'b1; e=1'b1; f=1'b0; g=1'b0;
end
else
begin: null
a=1'b1; b=1'b1; c=1'b1; d=1'b1; e=1'b1; f=1'b1; g=1'b1;
end
end
else
begin
=1'b1; b=1'b1; c=1'b1; d=1'b1; e=1'b1; f=1'b1; g=1'b1;
end
end
endmodule

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Verification:
Simulation:
The process of verification of functional correctness of the written code is called simulation
The above code is simulated and verified in the Xilinx Vivado design suite 14.2 for the exact
output. It needs an additional test bench to be written for the purpose of verification in which we
predefine the values.
Synthesis:
The process of mapping the implemented code onto a real world device is known as synthesis.
This is again done by the software
After the functional verification we have dumped the code into the hardware kit, Nexys 4 DDR
to verify the results on the seven segment display available on the kit
Output
The result of the above written code is as shown below:
Simulated output:

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Synthesized output
When i/p is 1001010 output represented as J When i/p is 01100001 output represented as a
When i/p is 0000000 output represented as 0 When i/p is 0000111output represented as 7

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Drawbacks:
In the above seven segmented display we cannot display few letters accurately for user
understanding, the user has to compromise between some letters such as W,X,K etc.
Conclusion:
The implementation of ASCII code to alphanumeric seven segment display has been performed
in the Vivado design suite and the simulated output is verified.
The Synthesized output has been performed and observed on the Xilinx Nexys 4 DDR FPGA kit
and the sample kit picture has been added to the project report.

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