Once students have gained insight through simulation of digital logic, they can continue this learning through deploying to Digilent Educational hardware.
This tutorial will provide an example of how students can create a Programmable Logic Design (PLD) and deploy this to Digilent hardware. The tutorial has been written using the Digilent Nexys 3 Board, but is the same process for all Digilent cards.
The Getting Started with Digilent Boards in Multisim tutorial will talk through the process for creating a PLD schematic for the Digilent board you are using.
- Create a new PLD schematic for your Digilent board. Details of this process can be found within the Getting Started with Digilent Boards in Multisim. During the creation choose to Uncheck all when selecting the IO terminals to include on the schematic.
- In this tutorial we are going to create an example that allows students to gain an understanding of the functionality of OR, AND and NOT logic gates. To add IO to the schematic, select either the input or output connector from the PLD toolbar. Click the input connector button.
- This will display the input connector dialog and provide a list of all the IO on the Digilent board that has been designated as an input. From the list select switch 0 (sw_0) and click OK. Place the terminal on the schematic.
- Repeat the process to add an input for switch 1 (sw_1).
- Using the output connector button, create an output terminal for LED 0 (LED_0).
- Open the Component Database (Right click > Place component), and place a 2 input AND gate.
Database: Master Database
Group: PLD Logic
- Repeat this process to add inputs, outputs, and logic gates to demonstrate the OR and NOT gates. This will create a schematic similar to the image below.
- Once the schematic has been created, we are ready to deploy the logic schematic to the Digilent board so students can physically manipulate the switches and view the response on the LEDs. Full details on deploying to Digilent cards can be found in the Getting Started with Digilent Boards in Multisim. Select: Transfer » Export to PLD from the menu bar. Here you will see the three export options. We want to export to physical hardware so select Program the Connected PLD. Click Next.
- Choose the Xilinx tool to compile the Multisim PLD design to a programming file. If you installed the Xilinx ISE Tools to the default location, they should autopopulate. If not, click the Xilinx tool drop-down menu, select Manually select tool, and then browse to the file folder where the tools were installed. The Xilinx user constraint file contains directions that map the connectors in Multisim to the pins of the Xilinx FPGA, Part Number XC6SLX16.
- At this point, you must connect the Digilent board to your computer. To check if all requirements have been met and the device is properly connected to Multisim, click the Refresh button. If the board is detected, the Device status displays Detected - Date and Time, as shown below.
- To proceed, click Finish. This begins the 11-step process of programming the PLD. Multisim automatically invokes the Xilinx ISE Tools (Creates the Xilinx project, Checks syntax, Translates, Places & Routes, Generates the programming file, and so on).
- Once the code had been generated and deployed to the Digilent board, the student can switch the switches and view the response on the integrated LEDs.
Using traditional teaching tools, a hands-on approach to learning Boolean logic is not possible until students have undertaken more advanced courses teaching them hardware description languages (eg. VHDL). Multisim simulation, PLD schematics and Digilent support provide an overall solution to allow students to learn through experimentation.