Discussions about Sinclair ZX80 and ZX81 Hardware
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siggi wrote: ↑
Tue Oct 10, 2017 9:34 am
Lardo Boffin wrote: ↑
Mon Oct 09, 2017 3:28 pm
Lots of nice little spaces ready for additional chips to maybe make it up to 64K?
The board itself may probably also be used for 64K ram modules. But AFAIK the Memotech rams contain a programmed chip (PROM?) for address decoding. So you would need to get the appropriate PROM for the 64K board....
IC5 is the "fast" PROM. Most of the Memotech boards I have seen use a device made by "MM", although I have forgotten the full name of the company
Needless to say, this PROM and others like it become obsolete many years ago.
I've got a datasheets somewhere for it.
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From our forum a link to http://www.zx81.de/memotech/memory64.txt
explains 64K function, the 4 dipswitch setting seem to be for setting 8-16K
Finish what you start. Truth is over the mountaintop or six feet under.
4 x TS1000, 2 x TS1500 , 2 x timex 2040 printer, 1/2 x timex 2020 cassette deck, ZXPAND, ZeddyNET, ZXBlast..., unfinished Spectrum...
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