On a Commodore 64, the computer is normally connected to a monitor with one composite video cable and to an audio device with a second, identical (although uniquely colored) cable. The signals passed through these cables are analog, each generated by a dedicated chip on the computer. Many C64 users may have accidentally swapped these cables when first setting up their machines, but [Matthias] wondered if this could be done purposefully — generating video with the audio hardware and vice versa.
Getting an audio signal from the video hardware on the Commodore is simple enough. The chips here operate at well over the needed frequency for even the best audio equipment, so it’s a relatively straightforward matter of generating an appropriate output wave. The audio hardware, on the other hand, is much less performative by comparison. The only component here capable of generating a fast enough signal to be understood by display hardware of the time is actually the volume register, although due to a filter on the chip the output is always going to be a bit blurred. But this setup is good enough to generate large text and some other features as well.
There are a few other constraints here as well, namely that loading the demos that [Matthias] has written takes so long that the audio can’t be paused while this happens and has to be bit-banged the entire time. It’s an in-depth project that shows mastery of the retro hardware, and for some other C64 demos take a look at this one which is written in just 256 bytes.
Thanks to [Jan] for the tip!
“so long that the audio can’t be paused while this happens and has to be bit-banged the entire time.”
Do you mean the audio that is video or the video that is audio?
90% connected the C64 trough a RF modulator to a TV set so never had this problem?
I must be the 10%.. the 1702 monitor rocked.
And it looked even sweeter when it was an Atari 800 driving it with S-video signals.
Most people I knew had monitors. Myself included. The only people I knew who hooked up to a tv were casual users.
That’s awesome!! I have tried connecting the audio to the monitor and composite to the stereo myself on the Amiga, but never tried to actually make a useful signal out of it on either output…
Now I wonder what happens if you uncross the cables, i.e. you accidentally connect audio to speaker and video to video, then run this demo!
Nice propwork btw.
256 characters includinh line numbers, produced this? 6 lines of code…
I’d like to see this impressive code.
No, that’s “some other C64 demos”. And written in machine code, not BASIC.
Very nice but I don’t remember the cables being so big.
Honey, i shrunk the user.
earlier i was reading rick moranis started in a relatively new sequel to honey i shrunk the kids called ‘shrunk’
Isn’t that Kraftwork?
What, no bouncing text? j/k nice demonstration.
Makes for a great ZX-81 emulator, too!
I remember playing around with an old C64 monitor years ago, hooking it up to a Casio keyboard and seeing what various sounds looked like. Nothing quite this impressive!
It’s Rammstein, isn’t it Heirate Mich?
“Excuse me Egon, you said crossing the streams was bad. You are going to endanger us. You are going to endanger our client, a nice lady who paid us in advance before she became a dog”
I can’t be the only one bothered by the low poly giant A/V cables 🤦🏼♂️. What’s terrible is many CAD programs smooth it on screen while the mesh is low poly. And it really doesn’t need to be.
Cool hack, very nice.