Lab 4 - Hex Calculator

Introduction:

In this lab, we will program the FPGA on the Nexys4 board to function as a simple hexadecimal calculator capable of adding and subtracting four-digit hexadecimal numbers. We will use a 16- buttom keypad to input hex numbers and the push-buttons on the Nexys4 board to act as operation buttons (+, –, = and clear). The results will be displayed on the four 7-segment displays on the Nexys4 board. The reason we build a hex calculator (rather than a decimal one) is that it makes the 7-segment display operation much simpler. Converting the output to decimal format would require a large amount of additional VHDL code.

Steps:

Keypad Interface :

We will be using a 16-button keypad module PmodKYPD (Figure 1) which plugs into one of the PMOD connectors on the Nexys2 board. The module and its connections are shown in Figure 1. The 16- buttons are labeled “0 1 2 3 4 5 6 7 8 9 A B C D E F”, so we can use this keyboard to enter numbers in hexadecimal format.

Hardware Setup :

Plug the PmodKYPD module into PMOD jack JA1 on the Nexys4 board. Note that the PmodKYPD uses all 12 pins of jack JA1 and must be connected with a 12 pin cable. Note the white alignment marks on the connectors. The alignment mark should be on the top-right for the connector attaching to the Nexys4 board and the top-left for the connector attaching to the PmodKYPD module.

Configure FPGA :

1. Using the same project settings from the previous labs, create a new project titled 'Hexcalc'.
   • Shown in Initial Project Setup in Lab 3
2. Create a new source titled 'keypad'
   • Shown in Initial Project Setup in Lab 3
3. Create another source titled 'leddec16'
4. Create a top level source titled 'hexcalc'
   • This is the top level that hooks it all together. This module:
     • Creates an instance of the keypad interface and 7-segment decoder interface modules
     • Make connection to the external keypad, display and buttons
     • Has a timing process to generate clocks for the keypad, display multiplexer and state machine 9
     • Implements a finite state machine to implement the operations of the calculator in response to button pushes.
5. Add an Implementation Constraint source file titled 'hexcalc'
6. Highlight the 'hexcalc.vhd' module in the Hierarchy window and run Synthesis
7. Run Implementation
8. Generate Bitstream
9. Plug in the device if it is not already and Vivado should detect the board
10. Click Program Device and load the generated bitstream onto the board
    • If you cannot click Program Device, click Open Target first

CalcultaBTNU (+)

BTNL(=)

BTNC(clear)

Helpful Resources:

How to set up the bitstream:

http://users.wpi.edu/~rjduck/Nexys4DDR%20Vivado%20VHDL%20Decoder%20Tutorial.pdf

How to Connect The Nexys A7 to your computer:

https://github.com/Digilent/Nexys-A7-100T-GPIO

Dr. Ackland's Lab Manual:

http://personal.stevens.edu/~backland/Courses/Course487_Spring_18_files/Labs/Lab4.pdf

GitHub:

https://github.com/kevinwlu/dsd