Sinclair ZX80 / ZX81 / Z88 Forums

This response is mainly for Rink but the points at the end might be of general interest. To be be fair the the changes in the iOS app store are no longer recent. For a while now Apple have allowed interpreted code to run on their iOS devices. There were restrictions on the languages that could be us...

PokeMon, Thanks for the extra info and link! Sirmoris, Love to expand the emulation to include zexpand in the future, thanks for the interest. I will find the time... The emulator is quite a long term project. Since I coincidently moved to Dundee three years ago, I have interviewed workers and shop ...

In my quest for improving the accuracy of the video emulation, I made an observation and hit a point that is still bugging me. Firstly, I noticed for the sudo hires Forty Niner game that the internal vertical window has to be up to around 21.3ms. If not, the program controlled vertical sync is not r...

Thanks to the replies on this thread I finally got something that resembles a loading screen. load1.png load2.png They don't quite match up to Pokemon's sample screens http://www.sinclairzxworld.com/viewtopic.php?f=7&t=1153 , but then I suspect there were some minor variations for sync pulse windows...

Again thanks for all your replies. So in summary (quick visual at the end of my lunch hour): overview.png As the shortest sync period that the IN/OUT instructions can generate is 11 processor clock cycles (22 video clock clock cycles), programatically generated pulses always have a length sufficient...

Thank you both for your replies. The information is just what I needed. I'll update my code this weekend and add the new images to this topic. A quick question: When a CRT display receives a sync pulse in the middle of video that is too short to trigger a horizontal retrace, would I be correct in ou...

Folks, I have questions about the generation of the ZX81 loading screen. Apologies for the following long winded background: I have been writing on and off an emulator since 2010. It differs from many in that the module/class to display the video is driven only by the three state video output (1v wh...

Well, this thread does seem to have reached the consensus/acceptance that the HYSNC is always running. So, to reiterate my questions from yesterday: 1) About which cycle should the emulator be in the 207 cycle loop after at the OUT ($FF),A releases the 3 bit ULA character row counter (LCNTRL)? Which...

Hmm - I am working on an extension for my video board - a sync generator to avoid loss of sync when ZX81 is running in fast mode. So I think in point no.4 you are maybe wrong. Sync generation is not permanently on and can (and will) be switched off when entering fast mode. PokeMon, sounds like an i...

Grant, Taking on board your findings regarding the free-running HSYNCs, for accuracy I reworked my main zx81 emulator loop to: - to incorporate the sync pulse for 16 cycles every 16 cycles into the 207 cycle loop - only have the cycle loop reset when INTACK would be generated in the central picture ...