Search found 2264 matches

by PokeMon
Sun Oct 30, 2011 5:29 pm
Forum: Sinclair Misc
Topic: Composite mod voltages
Replies: 104
Views: 46442

Re: Composite mod voltages

Yes you can. :lol: If you want a simple solution you can maybe use this version. But I do not guarantee that this is good for the ULA as it breaks down the white level to black in the back porch time. http://www.sps-wagner.de/Sonstiges/zx.html (german, you maybe translate this via google) This is th...
by PokeMon
Sun Oct 30, 2011 5:20 pm
Forum: Software
Topic: Check this out
Replies: 2
Views: 3108

Re: Check this out

Funny stuff. I didn't know that ZX81 was used for Karaoke in the early 80s. :mrgreen:
by PokeMon
Sat Oct 29, 2011 3:46 pm
Forum: Development
Topic: Clock doubling on ZX80... is it possible ?
Replies: 20
Views: 28841

Re: Clock doubling on ZX80... is it possible ?

Ok I accept that if you look at the video wave form it represents a 3.25Mhz squarewave... And therefor offer my appologies... But as they say the proof is in the pudding, so i rigged up a small test, checker board patterns Double speed pixels 1 piixel per 1/2 6.5Mhz clock cycle (on monochrome monit...
by PokeMon
Sat Oct 29, 2011 3:16 pm
Forum: Hardware
Topic: ZX81 with white screen
Replies: 2
Views: 2621

Re: ZX81 with white screen

I think this is the same like my ISS 3 bought over ebay as "untested". I think 90% of sold untested objects are waste. :mrgreen: I think the ULA is dead like mine and bring only sync pulses, no pixels. If you have a scope you can scan the signal. You will find the difference with working and non wor...
by PokeMon
Sat Oct 29, 2011 3:10 pm
Forum: Hardware
Topic: zx81 series differences
Replies: 16
Views: 7787

Re: zx81 series differences

hi All, Just a quickie - I was wondering how to tell the difference between zx81 versions simply on opening the box - I've no idea which series mine is and only realised there were differences from this site! That's easy I think when you only open the back cover. The name of the version is printed ...
by PokeMon
Sat Oct 29, 2011 2:41 pm
Forum: Sinclair Misc
Topic: Composite mod voltages
Replies: 104
Views: 46442

Re: Composite mod voltages

My modded Zeddy has ceased functioning. Voltages around the board seem OK but I have no image. The PD between earth and the pin on the composite output seems 2.6V DC, is that normal? Any chance I've fried the transistor? I guess this is a problem with missing back porch on video signal. Can you sim...
by PokeMon
Sun Oct 23, 2011 4:22 pm
Forum: Development
Topic: Clock doubling on ZX80... is it possible ?
Replies: 20
Views: 28841

Re: Clock doubling on ZX80... is it possible ?

you are simply wrong here, the pixels are output every 153.8ns ~ this IS a rate of 6.5Mhz, outputtung pixels at 1/2 cycles intervals at 6.5Mhz wouls result in a pixel frequency of 13.5Mhz ~ Sorry but you are wrong here. It is correct, that one pixel has a duration of 154 ns. The highest "frequency"...
by PokeMon
Sun Oct 23, 2011 2:08 am
Forum: Development
Topic: Clock doubling on ZX80... is it possible ?
Replies: 20
Views: 28841

Re: Clock doubling on ZX80... is it possible ?

64 chars per line and true interlaced display.... we are really getting out of ordinary TV world now... 64, 8 bit wide chars would be un-readable on a normal TV Andy No, I don't think so. Now you have 2x2 pixel for 1 pixel sent by ZX81 - or picture of ZX81 scaled by two when displayed on TV. 64x8 i...
by PokeMon
Sun Oct 23, 2011 2:02 am
Forum: Development
Topic: Clock doubling on ZX80... is it possible ?
Replies: 20
Views: 28841

Re: Clock doubling on ZX80... is it possible ?

Hmmm, quite interesting that Wiki... but... it seems that the 13.5Mhz you refer to is for digital sources, which probably explains why whenever i have connected the PC to a standard PAL tv the results are less than perfect... I also note that the Maximum video bandwith for any PAL system (J/K) is 6...
by PokeMon
Sat Oct 22, 2011 8:43 pm
Forum: Development
Topic: Clock doubling on ZX80... is it possible ?
Replies: 20
Views: 28841

Re: Clock doubling on ZX80... is it possible ?

And one more idea, what about using a 6 MHz version of Z80 cpu and no clock halfing ? Maybe you have to enter 4 wait states in that nop session but this could double Zeddy performance significantly. As datasheet it can be clocked up to 7,7 MHz (65 ns per clock high/low), so this would work with prop...