Thanks! I'll check this as soon as I get home to Sweden. The way my socket is configured, I most likely just ignored the PRG /CE and only used the /OE, which explains a lot of things. It's still kind of strange how my 16 byte long test program (which uses a loop to produce a sawtooth wave thru $4011) would run fine on it though. The unfortunate part is that this means I'll have to do an additional DIP-TO-IDC socket or start cutting up and rewire the damn board itself. =/ ...but at least I can try out some of the neat MMC5 features.