Pokemon made a RAM expansion which altered one of the first instructions of the ROM to start counting mem at +32k. It was genius. Making it count less (i.e. 1k) would be harder as you'd need to affect multiple bits IIUIC.
If you have an internal RAM, why not swap the ROM out - then you're in control of how the mem check works. You could have multiple images and a switch. I guess we're veering off into überzeddy territory now, though.
Issue 3 16k internal RAM mod
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Re: Issue 3 16k internal RAM mod
Certainly somewhat beyond my abilities! 

ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
Re: Issue 3 16k internal RAM mod
Here, Here!
Just sayin'
Upon closer look, I guess you meant switching ROMs not disabling mod
As I have always said make modifications that are switchable to stock operation if they are not otherwise transparent.If you have an internal RAM, why not swap the ROM out - then you're in control of how the mem check works. You could have multiple images and a switch.
Just sayin'
Upon closer look, I guess you meant switching ROMs not disabling mod
Last edited by gammaray on Sat Dec 23, 2017 6:53 pm, edited 1 time in total.
5-TS1000,UK ZX81<-Sheelagh, US ZX81, 2-TS1500/KDLX , 3-TS2040 printer, 2-TS2020 cassette decks, ZXPAND+AY, ZeddyNET, ZXBlast, UDG, ZX8CCB, AERCO, BUILDS/REPAIRS ZX Spectrum, ZX80 Minstrel, ZXMAX48 v1 v2, 2-TS-2068, ROM, 16kRAM
Re: Issue 3 16k internal RAM mod
Kind of late to the party, but here's another completed mod (click on image for full size):


No problem at all, here's the output of "PRINT PEEK 16388 + 256 * PEEK 16389" a.k.a. RAMTOP

That's 32768 -- I've got to get me a bigger monitor.....
No problem at all, here's the output of "PRINT PEEK 16388 + 256 * PEEK 16389" a.k.a. RAMTOP
That's 32768 -- I've got to get me a bigger monitor.....
Dan Moore
Portland, Oregon, USA
Portland, Oregon, USA