FPGA Lab 03: Numbers and Displays

Objective

Design a circuit to convert a 4-bit binary number (B[3:0]) into a two-digit decimal equivalent (D = d1d0).

Information

You are tasked with designing a circuit that converts a 4-bit binary number B[3:0] into its two-digit decimal equivalent D = d₁d₀. Table 1 shows the required output values. A partial design of this circuit is given in Figure 1. It includes a comparator that checks when the value of B is greater than 9 and uses the output of this comparator in the control of the 7-segment displays. Your task is to complete the design of this circuit.

Table 1: Binary-to-Decimal Conversion Values

The output gt signal for the comparator circuit can be specified using a single wire, with the four inputs B[3:0]. Design this Boolean expression by making a truth table that shows the valuations of the inputs B[3:0] for which gt has to be 1.

Figure 1: The Design of Binary-to-Decimal Conversion Circuit

Notice that the circuit in Figure 1 includes a 4-bit wide 2-to-1 multiplexer (a similar multiplexer was described as part of Lab 1.2). The purpose of this multiplexer is to drive digit d0 with the value of B when d1 = 0, and the value of r0 when d1 = 1.

To design the sub10 circuit, consider the following:

• For the input value B≤ 9, the circuit sub10 does not matter because the multiplexer in Figure 1 selects B in these cases.
• But, for the input values B > 9, the multiplexer will select r0 (the output of the sub10 module).

Thus, sub10 has to provide output values that properly implement Table 1 when the output result = 0001, …, and the input B = 1111 gives the output result = 0101. Design the sub10 circuit by making a truth table with the inputs bin[3:0] and the output result[3:0].

Step-by-Step Instructions

Perform the following steps:

1. Launch Intel Quartus Prime and create a new project:
   • Project working directory: <your project home folder>\Lab03.1_DisplayDecimal
   • Project name: displayDecimal
   • Top-level module name: displayDecimal
2. Create a new Verilog HDL file:
   
   • Implement the top module to Integrate the comparator, multiplexer, subtraction, and seven-segment display modules
   • Save it to the displayDecimal.v file.

   module displayDecimal(SW, HEX0, HEX1);
       input  [9:0] SW;
       output [7:0] HEX0;
       output [7:0] HEX1;
   
       wire    d1;
       wire    [3:0] d0;
       wire    [3:0] r0;
       wire    [7:0] seg0;
       wire    [7:0] seg1;
       wire    [3:0] B;
   
       assign B = SW[3:0];
       assign HEX0 = seg0;
       assign HEX1 = seg1;
   
       cmpGreat9    U1 (.bin( ), .gt( ));
       sub10        U2 (.bin( ), .ret( ));
       mux2to1_4bit U3 (.in0( ), .in1(), .sel( ), .out( ));
       sevenSeg     U4 (.bin( ), .seg( ));
       sevenSeg     U5 (.bin( ), .seg( ));
   
   endmodule
   

3. Create the comparator module:
   
   • Implement the comparator module that determines if the 4-bit binary number is greater than 9 or not.
   • Save it to the cmpGreat9.v file.

   module cmpGreat9(bin, gt);
       input  [3:0] bin;
       output       gt;
   
       // Using Gate-Level Modeling to implement this circuit
   
   
   endmodule
   

4. Create the 4-bit 2-to-1 MUX module:
   
   • Implement the 4-bit 2-to-1 MUX module that selects between the original binary number and the result after subtracting 10 if the number is greater than 9.
   • Save it to the mux2to1_4bit.v file.

   module mux2to1_4bit(in0, in1, sel, out);
       input  [3:0] in0;
       input  [3:0] in1;
       input        sel;
       output [3:0] out;
   
       // Using Dataflow Modeling to implement this circuit
   
   
   endmodule
   

5. Create the sub10 module:
   
   • Implement the sub10 module that subtracts 10 from the binary input if it is greater than 9.
   • Save it to the sub10.v file.

   module sub10(bin, ret);
       input  [3:0] bin;
       output [3:0] ret;
   
       // Using Dataflow Modeling (conditional operators) to implement this circuit
   
   
   endmodule
   

6. Create the sevenSeg module:
   
   • Implement the sevenSeg module, which converts the binary input to a format suitable for a seven-segment display.
   • Then, save it to the sevenSeg.v file.

   module sevenSeg(bin, seg);
       input  [3:0] bin;
       output [7:0] seg;
   
       // Using Dataflow Modeling (conditional operators) to implement this circuit
   
   
   endmodule
   

7. Compile the project:
   Use the Quartus RTL Viewer tool to examine the connections in the top module.
8. Download the circuit into an FPGA board:
   Test the circuit by trying all possible values of B and observing the output displays.