<65C02, because it was buillt in several conflicting versions. What about <the Z-80 core? Whose? Which one? Speed, of course, should be "limited" t <whatever was available in 1982. That certainly includes the Synertek (MOS In 1982 all of the z80s in the market had the same hidden features including the IX/IY 8bit ops. I know of no z80 that didn't have them. Not all of them were available to the 6mhz spec though many could be pushed. Also allowed is the 8085 (available as a 5-6mhz part then). Again all of the 8085s had the extra unsupported instructions as they were deem important! Allison