Search found 379 matches

by RetroTechie
Wed Apr 17, 2019 5:52 pm
Forum: Hardware
Topic: Zx81 from death to life??
Replies: 17
Views: 1132

Re: Zx81 from death to life??

@RS232: re-read my earlier post. You need to DOUBLE-CHECK modifications done since last working config. Looking closer at the pics, I noted: video signal comes from ULA (pin 16). Where to? Appears to be going nowhere. If indeed the case, then it logically follows that screen info doesn't make it to ...
by RetroTechie
Mon Apr 15, 2019 9:04 am
Forum: Hardware
Topic: Zx81 from death to life??
Replies: 17
Views: 1132

Re: Help my zx81 mod has gone wrong!! 8 bit death

I think i cracked it i tried one of these diodes and a 1W-100R resistor no idea if it means 100oms (..) Brown-black-brown = 1, 0, x 10^1 = 100 Ohm indeed. Doing mods like this, one should a) know this , and b) preferably verify using a multimeter before putting the part in. Anyway - good job! :D Di...
by RetroTechie
Sat Apr 13, 2019 10:42 pm
Forum: Welcome Area
Topic: Hello from Fort Worth, TX
Replies: 2
Views: 413

Re: Hello from Fort Worth, TX

Welcome here, Glenn! :) First I tested the 9VDC power supply (..) Toss that! Well, not in the bin, but back into the box where it came from. It's giving out a fairly high voltage with light load (with just a TS1000 hooked up, around 12V is not unusual), its capacitors will be in poor shape by now, a...
by RetroTechie
Sat Apr 13, 2019 10:04 pm
Forum: Hardware
Topic: Zx81 from death to life??
Replies: 17
Views: 1132

Re: Help my zx81 mod has gone wrong!! 8 bit death

When did you last get an image on screen from this ZX81? What mods where already on the board @ that time? What modification(s) did you do since then? A multimeter (voltmeter + something for checking connections between points on the board) is the very least you should have, I think. Modding a 35+ y...
by RetroTechie
Sat Apr 13, 2019 9:18 pm
Forum: Hardware
Topic: Zx81 from death to life??
Replies: 17
Views: 1132

Re: Help my zx81 mod has gone wrong!! 8 bit death

It's always possible that some component was damaged during handling of the board, in-between powerups to test things, ESD damage etc. But for the NMOS IC's in a ZX81: highly unlikely. If not that, following method is practically foolproof: start from last configuration that you KNOW 100% sure to be...
by RetroTechie
Sat Apr 06, 2019 11:02 am
Forum: ZX BASIC
Topic: Difference between New rom and Old Rom
Replies: 19
Views: 2219

Re: Difference between New rom and Old Rom

Thanks for your trouble Moggy! :)

Works as-is as ZX81 ROM (in emulators at least). Simply rename .p -> .rom or .bin as desired.
by RetroTechie
Fri Apr 05, 2019 7:38 am
Forum: ZX BASIC
Topic: Difference between New rom and Old Rom
Replies: 19
Views: 2219

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: 1009

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: 1009

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: 645

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...