Installing the world’s worst video card
Well here it is: This is perhaps my most-often requested video!
Everyone seems to want to see me take the breadboard “video card” I made and hook it up to a breadboard computer. So here we go!
I'm planning to release this video in about a week, so any feedback is greatly appreciated. I'm also going to release a new kit that includes all the parts for the video card at the same time. Part 2 of this video is about 80% done, so hopefully you'll see it pretty soon as well. I'm aiming for it to follow pretty closely behind this one.
Again, as always, thanks for your support and thanks for any early feedback on this video.
-Ben
Comments (21)
Is this the crudest form of DMA ("Direct Memory Access" or something)?
At 10:01 you say that the BE pin puts the bus in a low-impedance state, that should be HIGH-impedance right?
You briefly mentioned you could make it more complicated, but how much more complicated would it be to replace the ROM on the card with ram and only send data to the video card when the image changes. For example use a byte ( or even just a bit) in the io space to signal the image needs to change? And of course to add an other level of complexity, changing only the area of the screen ( or screen buffer) that need to change. Well maybe in a future segment of this series
This is a great video I've been waiting for! Another approach would be the way the Apple II did it. The video chips accessed the RAM during the high phase of the CPU clock when the CPU doesn't need it (or maybe it was the low phase...can't remember). Anyway, point is that the CPU and video card can share the RAM at the same time with no CPU penalty. You basically have RAM that runs at 2 MHz and the CPU/video just alternate clock phases. Brilliant approach! Maybe in a "Part 3" of this series, you could try that method?
At 13:50 when you're connecting the bus transceiver, you very briefly mention the difference between the chip series. I'd be interested in more detail about that.
This is awesome, nice to see you're releasing a kit for it at the same time. Have you considering putting together a kit for your "Learn how computers add numbers and build a 4 bit adder circuit" video seeing as it's your most viewed video? Could also include parts for your Digital Electronics series, latch and flip flop videos. Basically an introduction to digital electronics kit for those who want to get started with electronics and breadboarding but don't want to start with a big project.
Yeah, I definitely want to do this. I'd like to develop some additional materials to include in a beginner kit like this rather than it just being a box of parts, so that's the main thing that's slowed it down. But hopefully soon!
I think my first program to display something would clear the frame buffer then run munching squares. That wouldn't take advantage of the colour capability, though.
You should rename your channel to Ben’s Hack-a-thon! I can’t wait to see this thing output something. Are you going to flip us the bird image again or surprise us with something clever? Keep the great content coming!
71% overhead. 😱 Poor little 6502 sacrificing itself for the greater good.
Nooo.... not a cliffhanger! Looking forward to how this works out. Having the video and cpu running on different clocks could be a source for a lot of glitches. Might want to divide the 10mhz video clock down to 1mhz and run the cpu off of that. Maybe you cover that in part two. Thanks for doing this Ben, I know a lot of people (me included) have been hoping to see this.
Yep syncing the clocks is an issue for sure. The approach I'm taking is to run the timing-sensitive signal through a D flip-flop driven by the computer's clock. That way, changes to the output of the D flip-flop always happen on the next rising edge of the computer clock regardless of when the input to the D flip-flop changed.
OMG I’ve been waiting for this moment!! And it’s just as good as I’d hoped! 🤩 can’t wait to see that random ram contents flow through to a CRT 🤩
Also, that nice fancy box for the "the worlds worst video card" does that mean kits are available ?
This is great. Can we pre-order you videocard kit?
Love the blunt approach, keeps things simple :-) I wonder if a front and back buffer approach would also have been possible; definitely would gobble up more ram though.
Hi Ben, 10:00 "..puts the bus in the LOW (should be HIGH) impedance state..."
Ha, yeah low impedance isn't what you want :) Thanks for the catch.
Fantastic! Can't wait to watch!
Awesome! Are we going to be able to be the first to order the kit so we have a chance to get one before it sells out?
That's a good idea. I can plan to post a link here on Patreon in the next few days to pre-order before the video goes live. Thanks for the suggestion.