Generation of text on composite video

vivitern's picture
Last seen: 3 months 3 weeks ago
Joined: 11/14/2017 - 10:01pm

I'm building a homebrew computer. I want some way to get video out, preferably along the lines of 80x25 text. I'm not interested in framebuffer graphics.

Does such a thing exist as a single-chip text generation system, complete with clock, internal character generator ROM and video memory? Preferably speaking something like I2C...

Back in the old days there was the SAA5243( video generator, which did almost all of this. It would surprise me a lot if there wasn't something similar (but better) available today. I have found MAX7456 datasheet:, but that's really intended for OSD use and only does 30x16, which is a bit small. Is there any kind of modern equivalent?

Of course, I'm aware that any reasonably fast microcontroller can bit-bang composite video in software, but then I'd have to write it myself and I'd kinda like something which works.

(Incidentally, and this is not part of the question, but if anyone knows where I can get hold of an HD44780-style character LCD larger than about 80x16 I would be delighted.)

Update: Of course, anything that emits VGA is fine too. I basically want some form of video that's cheap and easy to display.

I'm using a microcontroller with no external RAM interface, so unfortunately that approach isn't viable.

I do have an external SPI RAM chip, and from looking at the datasheet it may be possible to persuade it to generate the pixel data: at the beginning of each scanline I'd prepare it for a read transfer, then output the CPU clock to the RAM's clock pin. That would mean a 16MHz pixel clock, which turns into 665x230 with PAL. (In order to write to video RAM I'd need to stop video refresh, however.) Did you have any cunning tricks in mind to avoid an interrupt every scanline?

filmywap2016's picture
Last seen: 3 months 3 weeks ago
Joined: 11/19/2017 - 12:10am

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