Search found 379 matches

by RetroTechie
Tue Jun 12, 2018 9:36 pm
Forum: ZX Spectrum Lounge
Topic: Any WoS admins on here?
Replies: 5
Views: 3984

Any WoS admins on here?

I'm in need of a wee bit of assistance... ;) Have been locked out of my World of Spectrum account for a while. Forgot how it happened, iirc logging in didn't work any more after updating my e-mail address. Since I don't post there often & was busy with other things anyway, went into read-only mode f...
by RetroTechie
Fri May 25, 2018 4:07 pm
Forum: SALES
Topic: SINCLAIR ZX SPECTRUM + 128K TOASTRACK RETRO VINTAGE COMPUTER
Replies: 3
Views: 1914

Re: SINCLAIR ZX SPECTRUM + 128K TOASTRACK RETRO VINTAGE COMPUTER

Agree on this one... :( I propose that users who only (or almost exclusively) use their account to post in the Sales section, be treated as spammers. And thus removed / blocked / banned / whatever. Above user would be a good example, just check this user's previous posts to see what I mean. Such use...
by RetroTechie
Sat May 19, 2018 12:02 am
Forum: Development
Topic: ZX81 ULA-in-a-CPLD
Replies: 233
Views: 62538

Re: ZX81 ULA-in-a-CPLD

what ram would i be enabling ? A 32K*8 SRAM used in a simple internal 16K RAM mod? Say, enabled in 2000-9FFFh range. Or mirrored all over the 64K address space except the lower 8KB occupied by the ROM? (that would also be nice when using a 128K*8 SRAM to fill the entire 2000-FFFFh range with unique...
by RetroTechie
Fri May 18, 2018 9:56 pm
Forum: Development
Topic: ZX81 ULA-in-a-CPLD
Replies: 233
Views: 62538

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: 1860

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: 5564

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: 5564

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: 8766

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: 4943

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: 1697

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...