EPROM selector - four EPROMs in one address range

EPROM selector elektor february 1985 Photograph. This shows the EPROM selector con- nected to the 6502 CPU board featured in the November 1983 issue of Elektor. EPROM four EPROMs in one address range byte hex dec. D1 DO EPROM 00001 11012 22103 33114 44001 55012 66103 77114 88001 99012 A 10 1 0 3 B 11 1 1 4 C 12 0 0 1 D 13012 E 14 1 0 3 F 15 1 1 4 Table 1. The relation between the EPROM enabled and the relevant software command. selector The main memory of a microcomputer has a remarkable property: when you buy the computer, the memory seems very large, but as time goes on it shrinks and shrinks, a phenomenon caused, of course, by your programs getting longer and longer... The circuit suggested here expands the memory but only insofar as EPROMs are concerned. Basically, it is a simple but effective "soft switch" which is suitable for all EPROMs in the 25XX and 27XX families. 2-52 Every computer user knows that it is not possible to just write data into an EPROM, but that this must ...