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Making a VGA Driver in SystemVerilog
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This article is a student's story about building a VGA display driver in SystemVerilog, a hardware design language, as a college lab project. It explains how old VGA screens were controlled and how the design counts pixels and timing.
What the project is
The author built a VGA driver for a class lab. A VGA driver is a circuit that tells a screen what to show, one pixel at a time. The author used an FPGA board, a chip that can be programmed to act like custom hardware. The project was hard, but the author says it was doable.
What VGA is
VGA (Video Graphics Array) is a display standard from 1987. Old screens were CRTs, which are big, heavy tubes. A CRT uses one electron beam that paints the picture one pixel at a time, moving line by line. Two signals, HSync and VSync, control how the beam moves across and down the screen. Our eyes blend the fast-moving dots into a full picture.
Key numbers
- Screen refresh rate: 60 Hz, meaning the full picture is redrawn 60 times each second.
- Pixel clock: about 25.175 MHz, so the screen gets pixels at that speed.
- FPGA board clock: 50 MHz, which is twice the pixel clock.
- Horizontal count: 640 visible pixels plus 160 off-screen pixels makes 800 in total.
- Vertical count: 480 visible lines plus 45 off-screen lines makes 525 in total.
Why it matters
This shows how timing works in digital hardware. The circuit must count carefully so the screen gets the right signals at the right moments. A simple trick, like turning a signal on and off every other clock cycle, can turn a fast board clock into the slower clock a screen needs. The article also shows why the design waits for the right time before showing color, so the old CRT is not harmed.
What to watch
- The next part of the article shows how the counter module is used to track a full frame.
- Watch how the HSync and VSync signals are turned on and off at the right counts.
- Look at how the interactive visuals show the simulation changing with each button.
Glossary
- VGA
- Video Graphics Array, an old display standard from 1987 that sends picture signals to a screen.
- FPGA
- A programmable chip that can be set up to work as custom digital hardware.
- CRT
- Cathode Ray Tube, an older kind of TV or monitor that paints a picture with an electron beam.
- HSync
- A signal that tells the screen when to move the beam to the start of the next line.
- VSync
- A signal that tells the screen when to move the beam back to the top to start a new frame.
- SystemVerilog
- A language used to describe digital circuits, like the logic inside a chip.