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Originally Posted by Slothie
While the 2114 is almost pin compatible with the 2111. the ground and write enable pins have been swapped and the 2 extra chip enables have been lost, so I'd have to add in some extra gates and it would be hard to add jumpers to cater for it due to the ground pin moving, so its one or the other rather than an option.
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I remember that the 2114 was different in terms of chip select lines and so on, but I am suggesting - maybe not on your initial V1.1 revision, but on V2.0, that you rearrange it so that it -only- uses 2114s since all of the 256-byte 4-bit types are becoming economically unobtainable.
Assuming you are still going to use BPROMs to hold the monitor code then you might consider using a third BPROM as a custom address decoder to generate with one IC the awkward chip enable intervals which would otherwise have to be generated with a 74138 plus more logic. (You may have your Tesla programmer up and running by that time).
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If I'm putting the address and data on the edge connector of course you could just leave out the 2111's and put in memory of your choice with logic that maps to the right places on an external card!
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Yes, Martin Lukasek has done that, except that he removes the original RAMs and plugs an overhead daughterboard into the SC/MP socket. It may depend on the PROM images at 0200 - 07FF already being absent (his replica is of the issue V PCB. I still have not established whether the issue V did or did not have this mod incorporated).
http://www.8bity.cz/2018/science-of-...ram-expansion/