Elf99 - rebirth of a classic

I'd rather use 24/28 pin JEDEC SRAMs because they are more standard and more widely available. Small ones also cost less than $5. I am not sufficiently versed in flash chips to consider designing one in. I am sufficiently well versed to include a 27xx EPROM. It's not the original 32x8 PROM, but it's close enough. If you'd seen the Elf-II schematic, I don't think you would have responded that way. I was never suggesting cannibalizing AT keyboards. They are entirely unsuitable. The original Elf-II has a keypad built up from individual pushbutton key switches, including several ones that latch up and down for LOAD, RUN and MEM PROT. The hex digits are latched through a (then) standard keyboard encoder chip. Most micros of the day used a software strobe keyboard or a byte-parallel ASCII keyboard. Neither approach would be suitable on the Elf because it's not running code at all when it's in loop mode - you, the user, DMA bytes in, one by one. The keyboard encoder is attached to the data bus through buffers. It's the only machine I know where the primary peripherals (keyboard and video) are all DMA. I was suggesting finding modern parts from a distributor of new or recycled (surplused) parts. I further suggested that modern replacements could run as much as $2 or $3 per switch (20 switches - 0 to F, R, L, P and I). The keypad was seen as an improvement over individual bit toggle switches, but even then, I saw it as an expensive hurdle that kept me from building an Elf-II. -ethan