Search found 363 matches

by RetroTechie
Fri Apr 05, 2019 7:38 am
Forum: ZX BASIC
Topic: Difference between New rom and Old Rom
Replies: 19
Views: 1409

Re: Difference between New rom and Old Rom

Anyone know where I can find a copy of the old/buggy ZX81 ROM? Some emulators include a ZX81 ROM, and @ one point long ago I typed in the bytes one-by-one from a real ZX81 into a floppy-equipped machine. But that's all the 'new' ZX81 ROM, don't seem to have the buggy version around. (sigh) is there ...
by RetroTechie
Mon Apr 01, 2019 2:38 am
Forum: ZX BASIC
Topic: what is the largest number that can be stored on a zx81
Replies: 10
Views: 544

Re: what is the largest number that can be stored on a zx81

Andy Rea wrote:so we have 16384 * 8 bits to store our large integer (..)
Ah, so you put your code in ROM, do away with screen output (or interrupts for that matter :? :?: ), AND keep all your counters in Z80 registers. That's pretty hardcore! :lol:
by RetroTechie
Sun Mar 31, 2019 5:55 am
Forum: ZX BASIC
Topic: what is the largest number that can be stored on a zx81
Replies: 10
Views: 544

Re: what is the largest number that can be stored on a zx81

Back when I was learning Z80 machine code on the ZX81 (and later the Spectrum), I came across a subject called Mersenne primes . In short: numbers in the form of 2^n -1 (for some specific values of n), that happen to be prime. Finding big Mersenne primes was of course :lol: the domain of supercomput...
by RetroTechie
Tue Jan 08, 2019 12:37 pm
Forum: Development
Topic: New year, new projects?
Replies: 2
Views: 454

Re: New year, new projects?

I'll surely be doing something in the area of ZX81 hardware this year. Haven't done so in a while, the 'itch' is getting stronger, pretty sure I can't ignore that for much longer. :D For public consumption (as in: you can read about the gory details): very likely. Putting something out as ready-to-b...
by RetroTechie
Wed Aug 15, 2018 7:27 am
Forum: SALES
Topic: ZX81 ULA
Replies: 65
Views: 14907

Re: ZX81 ULA

I wonder how long original ULA's would stay in working order if just stored under normal (+/- room temperature, not too dry or moist air, no direct sunlight etc). Let's say, starting with little used or N ew O ld S tock parts. Maybe power up once or twice a year (under carefully controlled condition...
by RetroTechie
Wed Aug 15, 2018 6:53 am
Forum: Hardware
Topic: PSU Voltages.
Replies: 5
Views: 1276

Re: PSU Voltages.

Power supplies using a transformer, rectifiers and smoothing capacitor(s) were very common before the cost of switch mode power supply technology fell in price. DC voltage regulation is very often used inside equipment. Practically required for digital circuitry. Before switch mode psu's became the...
by RetroTechie
Sat Aug 11, 2018 3:01 am
Forum: Hardware
Topic: PSU Voltages.
Replies: 5
Views: 1276

Re: PSU Voltages.

Yes it's common actual supplied voltage is much higher than the nominal of about 9V (both for Spectrum and '80/81). But no-load voltages aren't very useful. Measure under load. High input voltage does not directly influence operation (since internal voltage regulator), but it does affect how much wa...
by RetroTechie
Thu Jul 26, 2018 2:49 am
Forum: SALES
Topic: Fakeness overload
Replies: 0
Views: 2260

Fakeness overload

We all know that fake parts are a common problem on eBay and similar sites. But sometimes you run across an item where the "L@@K FAKE!!" is so thick it's funny. Not to mention lack of knowledge on behalf of the seller: :lol: 14,Z84C0020PEC Z84C0020 NMOS/CMOS Z80 CPU CENTRAL PROCESSING UNIT DIP-40,NR...
by RetroTechie
Fri Jul 20, 2018 10:33 pm
Forum: Sinclair Misc
Topic: Ferranti ULA doc may be of interest
Replies: 12
Views: 3388

Re: Ferranti ULA doc may be of interest

Pretty useless in practical sense. But nice reading material anyway. :D now then if any is clever enough to decap a ULA and photograph the final layer, it would be possible to reconstruct the exact logic hiding inside the little vlack chip :mrgreen: Getting at the bare IC die isn't the hard part... ...
by RetroTechie
Thu Jul 05, 2018 10:21 pm
Forum: Sinclair Misc
Topic: Z80 CPU part number cross reference
Replies: 1
Views: 583

Z80 CPU part number cross reference

Hello all, I've compiled an overview that (apart from speed and package) includes all Z80 CPU's you're likely to come across. Including 100% plug-in compatibles, NOT including almost-compatibles-with-a-few-added-pins, or pin-compatible-with-internal-additions (read: that are not a 100% functional eq...