Elf99 - rebirth of a classic

From: Ethan Dicks <erd_at_infinet.com>
Date: Mon Nov 9 23:46:47 1998

 
> > I originally wrote:
> > > < How authentic should a modern Elf be? Try to use 1822/2101 RAM or use
> >
>
> Better use widely available SRAMs like you see on motherboard caches
> in DIP packages? One 64K x 8bit chip cost $5 at any speeds low as
> 15ns but it will work in 400ns cycle time machines.

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.

> Better design the circuit to accept standard memories, ROM's also
> preflashed flash chips in place of ROM's as a suggestion.

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.
 
> > The problem with replicating the SuperElf is the keyboard. I have no
> > idea where to get that chip from (74941?), nor an inexpensive source
> > for that many pushbuttons (including some latching ones).
 
> Make a standard keyboard convertors based on PIC ic to spit out ascii
> binary using standard AT and PS/2 keyboards? That is far easier than
> trying to scrap already valueable stuff for needed parts and
> suitable "old" keyboards is hard enough to find already as is.
> $10 dollars keyboard and a $20 worth of that little converter kit is
> appealing I think.

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
Received on Mon Nov 09 1998 - 23:46:47 GMT