We have become accustomed to computers with displays, but how many people have created circuits that directly drive one? Of course, we have already written the SPI display driver on the microcontroller, but create the hardware to generate a usable video signal? This is a bit difficult. [Jdh] But I have tried, With TTL video card.
In this case, it is not a card, but a set of breadboards, but all the logic is there to generate the complex video timing array required for synchronization, and output the bits in the correct voltage level sequence for the analog monitor use. It is worth pointing out that it is not the composite video signal being created because it is monochromatic and has no subcarriers.
The last problem he encountered was that the pixel rate of his ROM was not fast enough, so the image had artifacts, but it at least produced something recognizable and readable on the screen. Veterans in the video industry may point out that analog TV is a bit tolerant in terms of precise timing and line count, so it is possible to simplify the circuit, and sacrificing some resolution may solve the ROM speed problem. But this is an impressive work, and anyone interested in how video works should be of particular interest.
Fans of graphics cards on breadboards should also check out [Ben Eater’s] 7400 series graphics cards.
thanks [Måns Almered] tip.