Elf99 - rebirth of a classic

From: jpero_at_pop.cgocable.net <(jpero_at_pop.cgocable.net)>
Date: Tue Nov 10 07:20:21 1998

> Date: Tue, 10 Nov 1998 00:46:47 -0500 (EST)
> Reply-to: classiccmp_at_u.washington.edu
> From: Ethan Dicks <erd_at_infinet.com>
> To: "Discussion re-collecting of classic computers" <classiccmp_at_u.washington.edu>
> Subject: Re: Elf99 - rebirth of a classic

>
> > > 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.

These are!

Often I have to test motherboards also those ones equipped with flash
chip using an specialiazed diagnostic card and a speical set of bios.
Those bios is 27512 type and have similar pins and fitted into
32pin socket still works, ditto for 1024bit ROM's and flash 29010
chips. Sometimes I have to use that same special tool pair of
roms "27512" on older 27128 or 27256 pair motherboards.
 
All of these docs can be found on 'net from AMD, intel, for these
info you need.
 
> 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_at_cgocable.net
Pero, Jason D.
Received on Tue Nov 10 1998 - 07:20:21 GMT