Search found 57 matches

by kpalser
Sun Jul 28, 2013 12:51 pm
Forum: Emulators
Topic: Help with ZX81 loading screen for new emulator
Replies: 18
Views: 4087

Re: Help with ZX81 loading screen for new emulator

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...
by kpalser
Tue Jul 02, 2013 3:20 pm
Forum: Emulators
Topic: Help with ZX81 loading screen for new emulator
Replies: 18
Views: 4087

Re: Help with ZX81 loading screen for new emulator

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...
by kpalser
Mon Jul 01, 2013 7:11 pm
Forum: Emulators
Topic: Help with ZX81 loading screen for new emulator
Replies: 18
Views: 4087

Re: Help with ZX81 loading screen for new emulator

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...
by kpalser
Mon Jul 01, 2013 12:09 am
Forum: Emulators
Topic: Help with ZX81 loading screen for new emulator
Replies: 18
Views: 4087

Help with ZX81 loading screen for new emulator

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...
by kpalser
Mon Jun 04, 2012 12:33 pm
Forum: Development
Topic: How the ZX81 NMI / sync works... my 10 points
Replies: 19
Views: 9885

Re: How the ZX81 NMI / sync works... my 10 points

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...
by kpalser
Mon Jun 04, 2012 2:00 am
Forum: Development
Topic: How the ZX81 NMI / sync works... my 10 points
Replies: 19
Views: 9885

Re: How the ZX81 NMI / sync works... my 10 points

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...
by kpalser
Sun Jun 03, 2012 2:24 pm
Forum: Development
Topic: How the ZX81 NMI / sync works... my 10 points
Replies: 19
Views: 9885

Re: How the ZX81 NMI / sync works... my 10 points

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 ...