ULA Video Out questions

[PokeMon]

Does anybody know what kind of ULA is used for the Timex TS 1000 or the TS 1500 ?
Is it just the same ULA C210 or did Sinclair use a new/different one ?
I wonder about the voltage of the video output at #16.

[Andy Rea]

The TS1000 just used an ordinary ULA as found in ever other ZX81.... The TS1500 on the other hand had it's very own custom chip.....

[blittled]

I was rereading this thread I had an epiphany. Instead of using an ADC chip why not just use a simple op-amp voltage comparator with the output tied to a transistor to switch the proper logic voltage levels. The comparator would have to be set high enough to have the back porch in Rev 3 be considered a low so all 3 versions would work. A 3.25V regular that I plan to power the micro-controller should be a good voltage reference.

I would then tie it to a Propeller since it can sample at intervals as fast as 12.5 nSec which should be sufficient to capture the conditioned pulses. The trick will be locking onto the sync pulses so I can recreate the bytes from the video stream. The Propeller actually has 16 video generators in it so I could simply transfer the reconstructed bytes out one as a 2 color stream with front and back porches included so it would work with any AV input that uses NTSC. I'm in the USA so I don't have access to a PAL based TV.

I hope to also store the stream into memory so another video generator could display VGA as well. I envision having a box that takes in the video and outputs the same video (for ZX81 purists), a reconditioned video out and a VGA out. It will also have three buttons to let you cycle through available foreground and background colors and a color set button to keep the selected colors.

I need to work on another project for a friend so that hopefully he'll help me build a version with a pcb for this. In the meantime I'll breadboard it to see if my idea works and I'll use this thread for any updates.

[sirmorris]

Good luck!

[blittled]

I posted my new idea on the Parallax Propeller forums to get advice from some of the video gurus on the site. The response was that it would be very difficult since you have a window of time to do 4 Propeller assembly instructions per pulse detection. Also some sort of external synch detector needs to be added. They are on the verge of producing the Propeller II with enhanced features and speed that may be more capable of handling this.

They also offered ideas very similar to what Pokemon is doing or polling the control signals,address and data lines as I originally looked into.

[PokeMon]

By the way, the front porch isn't really important. It is just the back porch which gives the black color reference voltage level.