osiweb.org

I have a heavily modified C1/P, which was my very first computer. Almost as soon as I got it (early 1982), I started poking around inside to see how it worked. Here's a list of some of the mods.

CEGMON
Tape-interface speed up to 1200 baud
Guard-band kit to get all the characters on screen
Overclocking to 2MHz, then to 3MHz after an upgrade to a 65C02 and consolidating all the ROMs into a single faster EPROM. A bit temperamental, but worked most of the time, on a cool day.
Designed my own programmable character generator, which allowed pseudo-bit-mapped graphics.
Designed a 19" rack expansion called "Ozrak", a play on "Orac" from the Blake's 7 TV series. A/Ds, 16K DRAM, lots of PI/O ...

I'd like to get it back up and running, but don't have a monitor that will display interlaced video with PAL timing. I was thinking of modifying the video circuit to produce progressive video instead, was looking at the circuit diagram and had completely forgotten about the colour RAM!! Which lead me to Google 630 I/O expansion ... which lead me here!!

So hello! Fellow OSI / UK101 fans.

Welcome! It would be great to hear more about your mods. I had a C2-4P, and also did a programmable character gen, along with other graphics projects. It would be cool to compare notes.

Dave

Nice!

These are such great machines for those with fertile minds!!

Slartybartfast wrote: ↑Sat Oct 03, 2020 2:58 pm I'd like to get it back up and running, but don't have a monitor that will display interlaced video with PAL timing.

Although I'm not very familiar with the PAL version, it seems to me that none of these systems actually put out interlaced video; my Amiga was the first (only?) computer I ever had that would do that on a regular basis. A Wikipedia article on interlaced video suggests the scanning modes of early computers like OSIs would be referred to as "240p" (NTSC) or "288p" (PAL) in today's terminology.

So by your description, your display is probably not capable of PAL timing even if the signal is progressive. Do you already know your display doesn't work with some other PAL signal, or are you assuming that PAL is the problem? Because it's easily possible that the video output circuitry might not have aged gracefully.