+OLD CS1 Posted March 29, 2015 Share Posted March 29, 2015 I have a 1750 REU with a very simple switch modification to the board. My guess is this is to switch between base address of $DE00 and $DF00, or it may be to turn the empty ROM socket on and off. I dunno, but does anyone recognize this mod? Quote Link to comment Share on other sites More sharing options...
+sm3 Posted March 30, 2015 Share Posted March 30, 2015 I believe that is the J2 jumper. It's used to select the size of the ROM you can put in that open slot 16k or 32k Quote Link to comment Share on other sites More sharing options...
+OLD CS1 Posted March 30, 2015 Author Share Posted March 30, 2015 I believe that is the J2 jumper. It's used to select the size of the ROM you can put in that open slot 16k or 32k Interesting. Considering this unit has no ROM (came that way,) I wonder what might have occupied that space before I got it. I do not see any wear on the socket so whatever it was must have been fairly permanent. Into what address space does that ROM decode? Quote Link to comment Share on other sites More sharing options...
+sm3 Posted March 30, 2015 Share Posted March 30, 2015 Some apparently have the socket and some don't. If you look at your 128 memory map, the internal/external ROM should be at the same locations. It just depends on the bank configuration and what size ROM you have as well as some additional jumper settings. Quote Link to comment Share on other sites More sharing options...
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