EPROM emulators (was Re: newbie building a scratch-built computer)

Btw, for an ultra-simple EPROM emulator, use one of the Dallas NVRAM chips (DS1225 (8K) , DS1235 (32K) etc.). Stuff it in a RAM socket of a convienent SBC to program it, and make an adapter by piggybacking a couple of sockets and moving the necessary address lines, mask write etc. to plug it into a ROM socket. One "gotcha" - the internal reset circuit of the Dallas parts trips at a higher voltage than most "resistor and cap" reset circuits, which means your "ROM" isn't present when the processor starts executing - Manually resetting it shortly after power-on works in these cases. I've used this technique on many occation to shorten eprom erase/burn cycles during near-final testing. I've also got a Tech-Tools "EconoROM" which connects to PC via parallel port and works very well as a load and reset on the fly device. Handy in the earlier stages when reloads are frequent. It supports 2764-27512, and I've made adapters to use it in smaller sockets. Dave -- dave06a (at) Dave Dunfield dunfield (dot) Firmware development services & tools: www.dunfield.com com Collector of vintage computing equipment: http://www.classiccmp.org/dunfield/index.html