Search found 376 matches

by RetroTechie
Fri May 18, 2018 9:56 pm
Forum: Development
Topic: ZX81 ULA-in-a-CPLD
Replies: 233
Views: 43917

Re: ZX81 ULA-in-a-CPLD

Great progress Andy! Looking good! :D oh my :geek: the link in the middle is mighty close to touching the case ... the easiest thing would be to fit a right angle header. (might have to bend it up slightly :? ) Personal opinion: put feature jumper(s) on a side end of the board. One pin solders to to...
by RetroTechie
Sun May 13, 2018 12:13 am
Forum: Hardware
Topic: Gigatron - TTL microcomputer
Replies: 4
Views: 1253

Gigatron - TTL microcomputer

Hi, anyone stumble across this already? A simple 8 bit micro, with an EPROM and SRAM chip as main memory, but using only TTL chips for the CPU. 8-) :ugeek: (74HCT actually, for those of you playing along at home ;) ). Homepage: https://gigatron.io/ Aussie electronics boffin Dave Jones just did a rev...
by RetroTechie
Wed Apr 18, 2018 6:19 pm
Forum: Welcome Area
Topic: Hello from Canada
Replies: 17
Views: 3733

Re: Hello from Canada

Hmm too hot to touch though? It seems to be giving out more then 5V closer to 7 Or measuring wrong - seen often when people (try to) check voltages. For 78xx regulators like the 7805 in the photo, seen from the front (printed) side, pins from left to right are input, GND, output. So you'd put your ...
by RetroTechie
Sun Apr 15, 2018 3:02 pm
Forum: Welcome Area
Topic: Hello from Canada
Replies: 17
Views: 3733

Re: Hello from Canada

Much preferable over a RAM pack: https://web.archive.org/web/20150905141235/http://bitcycle.org/retro/zx81/internal_RAM/ Cheap, fairly easy, no RAM pack wobble, edge connector remains free for other add-ons like sound card, flash card storage etc. The original 16K RAM packs were poorly designed & an...
by RetroTechie
Wed Apr 11, 2018 11:05 am
Forum: Hardware
Topic: ZX81 I/O interface for your projects
Replies: 27
Views: 6558

Re: ZX81 I/O interface for your projects

74HC -> 74LS: no problem, unless you're driving many LS inputs at once. In that case check datasheets / calculate load currents etc. 74LS -> 74HC: often works fine. In general, just check properties of IC where a signal comes from (and check datasheet of the HC part where it goes to). Better: add a ...
by RetroTechie
Sun Apr 01, 2018 1:15 am
Forum: Hardware
Topic: Tape read/write on expansion port?
Replies: 24
Views: 3386

Re: Tape read/write on expansion port?

You must remember for port $FE to work correctly you use open collector drivers only.. DO NOT DRIVE DATA LINES HIGH. So you see the ula can if it's wants drive a data line low , or an external device can drive it low. High is created by the pull-up when nothing drive it low. Commonly known as " wir...
by RetroTechie
Thu Mar 29, 2018 2:51 am
Forum: Sinclair Misc
Topic: Why the difference in TV out port?
Replies: 2
Views: 1120

Re: Why the difference in TV out port?

At least for the TS1000, RF (TV) output is on V HF channel 2 or 3. Versus U HF channel 36 on a regular (UK) ZX81. Also note the channel select switch on the bottom, which is not present on a UK ZX81. And the somewhat-conductive silvery paint + metal strip inside the case on US models (for EMI shield...
by RetroTechie
Sat Mar 24, 2018 4:52 pm
Forum: GAMES
Topic: Looking for a game
Replies: 6
Views: 1151

Re: Looking for a game

You might also want to check out "Damper", aka Colour Clash on the Spectrum. Download here:

www.zx81.nl/dload/software/d/
by RetroTechie
Fri Mar 16, 2018 1:42 am
Forum: GAMES
Topic: Copyrights for New Generation Software games (e.g. 3D Monster Maze)
Replies: 5
Views: 1403

Re: Copyrights for New Generation Software games (e.g. 3D Monster Maze)

This might be the worst advice ever, but: you could always just publish it and see what happens. Second that. If "just remove offending title if a copyright claim is received" works for you, then why not just go ahead. Ah yes, the -mostly theoretical- risk of legal problems / monetary damages etc. ...
by RetroTechie
Wed Mar 14, 2018 2:14 am
Forum: Development
Topic: do we still use UHF modulators ?
Replies: 17
Views: 2330

Re: do we still use UHF modulators ?

Looks like close to standard composite voltage levels the modulator wants, apart from a DC bias (say, series capacitor or so?). Sadly there's no info on typical input impedance for that modulator. :?: it does mean that broken zeddies which are not comp modded won’t be fixable with this ULA (..) Quit...