FPGA VAX update, now DIY TTL computers

woodelf wrote: Which is what I don't understand from my experiences with my own CPU long ago. 16 bit would be okay and maybe even more bits, but I decided against classical 4, 8 or 12 bits those days, although these sizes were quite popular then for "real" CPUs. The point is that I didn't want to have sophisticated instruction decoding logic, this disallowed multiple word instructions. I knew about microprogramming, of course, but this were out of reach because of lacking facilities to burn PROMs (I was a pupil then). For memory addresses and immediate operands, this meant a single instruction should hold enough address or data bits. With 12 bits you are restricted to too few possible instructions or too few address bits (4 bit instruction or 8 bit address/immediate data was not enough for my ambitious plans. 16 bit were suitable even if it required two "load immediate" instructions (for the low and the high byte). However the first architecture had 16 bit instructions but an 8 bit data path only (except the separate 12 bit address increment/index logic). Holger