Chapter 9: A Better Way to Display – VGA

Up until now, we've been limited to displaying information using LEDs, single color or RGB, as well as the 7-segment display. We are quite capable of performing operations and displaying limited information, as we have demonstrated with our temperature sensor and calculator. The Nexys A7 offers an additional output that can provide us with an almost unlimited method of displaying information, the Video Graphics Array (VGA) connector. The VGA connector on the Nexys A7 can display resolutions of up to 1600x1200, with up to 2^12 or 4,096 colors. What allows us to unlock this capability is that we now know how to use our external memory, which will provide our framebuffer.

By the end of this chapter, we'll have created a method of displaying data on a Cathode Ray Tube (CRT) or LCD monitor via the VGA connector. In Chapter 10, Bringing It All Together, we'll use this methodology to upgrade some of our projects to utilize...

Technical requirements

The technical requirements for this chapter are the same as those for Chapter 1, Introduction to FPGA Architectures and Xilinx Vivado.

To follow along with the examples and the project, you can find the code files for this chapter at the following repository on GitHub: https://github.com/PacktPublishing/Learn-FPGA-Programming/CH8.

A VGA-capable monitor and cable are also required if you want to implement the project on the board.

Project 11 – Introducing the VGA

The earliest professional computer displays were simple monochrome text displays. The earliest personal computers, such as the Apple 2, could display 280x192 pixels with a small number of colors. The Commodore 64 and IBM/PC could display 320x200, again with limited color palettes. The original IBM VGA was introduced in 1987 and it allowed for higher resolutions and standardized the connector going forward until digital displays such as LCDs became the norm.

The first thing we'll need to look at is how the screen is drawn. Whether you are using a CRT display or a modern LCD, the timing is still supported to provide backward compatibility. Originally, the VGA output was designed to drive an electron gun to light up phosphors on a CRT. This meant timing spanned the entire display, plus time for the gun to shift from one side of the screen to the other, or from the bottom back to the top. Figure 9.1 shows the various timing parameters and...

Summary

In this chapter, we've introduced a better way of displaying data. Previously, we were limited to the physical outputs: a row of 16 LEDs, two tricolor LEDs, and the 7-segment display. We made good use of them for the simple testing of logic functions, our traffic light controller, and our simple calculator. We've used a ROM to display text. We've introduced a programmable PLL and used our DDR2 controller. We're now ready to tackle our capstone project.

In the next chapter, we'll wrap up the book by putting everything together. We can use our VGA to display the output from our temperature sensor, calculator, and microphone. We'll also introduce the PS/2 keyboard interface to provide an easier way to control the system.

Questions

1. You can use an XOR gate as:

   a) A way to add two bits

   b) A way to multiply two bits

   c) A programmable inverter

2. We are limited to what resolution when generating a VGA controller?

   a) 640x480 @ 60 Hz

   b) 1280x1024 @ 85 Hz

   c) 1920x1200 @ 60 Hz

   d) A resolution our monitor can handle and a pixel clock that we can reliably meet timing for in our design

3. Building a VGA controller in an FPGA is impractical.

   a) True

   b) False

4. How many colors can we represent with 888 or 24 bpp?

   a) 2 colors

   b) 16 colors

   c) 64K colors

   d) True color, or 16 million colors

5. An AXI Lite write interface consists of which of the following?

   a) A write address

   b) Write data

   c) A write response

   d) All of the above

6. An AXI Lite read interface consists of which of the following?

   a) A read address

   b) Read data

   c) A read response

   d) All of the above

   e) (a) and (b)

Challenge

The current VGA design only displays black and white. Can you change the design to display two different colors? Can you modify it to use some switches on the board to select these colors?

Further reading

For more information about what was covered in this chapter, please refer to the following links:

• https://www.xilinx.com/support/documentation/ip_documentation/clk_wiz/v6_0/pg065-clk-wiz.pdf
• https://glenwing.github.io/docs/VESA-DMT-1.13.pdf