9 Nov
1998
9 Nov
'98
11:20 p.m.
Date: Tue, 10 Nov 1998 00:46:47 -0500 (EST)
Reply-to: classiccmp(a)u.washington.edu
From: Ethan Dicks <erd(a)infinet.com>
To: "Discussion re-collecting of classic computers"
<classiccmp(a)u.washington.edu>
Subject: Re: Elf99 - rebirth of a classic
I
originally wrote:
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. < How authentic should a modern Elf be? Try
to use 1822/2101 RAM or use
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.
True, but best to keep things easier and more fun, you need to make
do with current avaiable comonents not relying on used or no longer
made parts. That really crimps anyone's fun if can't find the part
or that part costs more than 10 each aside from CPU's.
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.
Yeah, you should had said that "DMA" then I would understood! :-)
Make an design and make it work instead of relying on that no longer
made chip even use PIC or multiple IC's?
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.
Keypad okay, but the "special" chips that is right now on no longer
made and hard to find is not fun. Make it easier for these following
people. There are many users who prefers to use it to explore
the CPU and program with it instead of hacking at hardware level.
-ethan
Jason D.
email: jpero(a)cgocable.net
Pero, Jason D.