The Challenge

From a prior project you already know that any decimal digit from zero through nine can be displayed by lighting the appropriate segments of a 7-segment display, as shown in Figure 1.

THE SEVEN-SEGMENT DISPLAY

Figure 1: Segment definitions of a 7-segment display.

In Project Six, the design was limited to displaying one BCD digit on a seven segment display.  Project Five resulted in a multiplier design that produces an 8-bit binary number as the output. Displaying such numbers in the human readable decimal format using multiple seven segment display units is thus essential. Project Seven requires you to design and implement a circuit to display an 8-bit binary integer using 7-segment displays using ROM.

With 8-bit inputs however you no longer will be able to simplify the equations using K-maps; optimization of solution using algebraic equations in a reasonable time is not possible either. Therefore, an 8-bit   binary to seven-segment decoder is a good candidate for a ROM based design.

Specifications:

1. The input is an 8-bit binary number [I7,...I0] (use switches 0-7 on your DE-2: SW7= I7 (MSB), .... SW0=I0 (LSB).
2. Use a 256x24bit ROM. No additional logic gates may be used.
   
3. The output is displayed on three seven-segment display units. The inputs to the three 7-segment display units, from left to right, are denoted by [A2,B2, ...G2], [A1, B1, ...G1], and [A0,B0, ...G0] respectively.
   
4. Use a push-button on DE-2 to manually generate a clock pulse for reading the ROM.
   
   

Description:

Figure 2 illustrates the ROM based design. To display all possible 8-bit combinations, three seven segment displays are needed.
For example, when the input binary pattern [I7,....I0] = 1000 0001  is applied, the display should indicate 129, with 1 in the left display, 2 in the middle display and 9 in the right display. Since [I7, ...I0] serves as the address of the ROM, location 1000 0001 of the ROM should contain the 24-bit  pattern   [X2,G2, F2,E2, D2,C2,B2,A2,  X1,G1,F1,E1, D1,C1,B1,A1,  X0,G0,F0,E0, D0,C0,B0,A0] corresponding to 129. Since the displays need only 21 bits, and the ROM is 24 bits wide, assume that three bits X2, X1, X0 in the memory are set to 0.

Refer to the DE-2 Manuals regarding how to enable a specific digit on this display. Note: Applying a logic low level to a segment causes it to light up and applying a high level turns it off.

 

  Figure 2:  ROM based design of   8-bit binary to seven-segment decoder circuit.

Procedure:

• Create or be prepared to create a file containing the contents of the ROM to solve this problem. Rather than entering the binary characters, enter the strings using Hexadecimal. 
• Grab the ROM generator here. To use it, follow the instructions in the procedures link below to generate the .mif file. Instead of following the instructions in the procedures link to enter the values into each ROM address individually, open the ROM generator and enter your calculated values into column K. The ROM contents will be generated in the top left portion of the spreadsheet. Copy the ROM contents on the left and paste it into your .mif file.
• Using Quartus-II create the schematic. Following link provides additional information on the procedure to carry out this project.
• Simulate it with input patterns 50 through 75.
  
• Implement this hardware on your DE-2 Board and test it.

REPORT

Prepare a memorandum which is addressed to the manager of the R&D group at Banana.   Go to the Preparing the Memo link to review the general requirements for Banana Memos or to the What to Include and Grading Policy  link for the specific things to include in the Project #7 report.

_______________