15 Jun
2008
15 Jun
'08
7:12 p.m.
bfranchuk at jetnet.ab.ca bfranchuk at jetnet.ab.ca
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ew%20computer%20circuit%20board.htm&In-Reply-To=CAD07A50FEA44B73BFD2864883FC
644B%40andrewdesktop>
Sun Jun 15 20:05:45 CDT 2008
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________________________________
Andrew Lynch wrote:
That means compromises had to be made and some stuff
had to go.
Anyone can design a great computer on paper. Making a real, tangible part
is a lot more difficult.
Using cool sounding but almost impossible to find parts seems easy but it
makes the SBC practically worthless.
If you can make a low cost Z80 SBC that includes floppy IO, I would love
to
see it. I'd even buy one or two.
But when you think about it, most early CP/M machines were
8 inch single density. Not much on a disk and that I think is
the basic format to look at. I think I seen a data separator
using a 16 bit counter at 4x? the data rate but I can't remember
where.
I look forward to seeing your design.
Thanks and have a nice day!
I can't say I am having a nice day.
I am still grumbling over not getting PAD's
PCB and LAYOUT software when I could in
the late 80's. I am looking to do a 16 bit
(2901) cpu using EEPROM (2kx8 250 ns)
and am still trying to find a schematic capture
and PCB layout program that I can afford
with through the whole parts.
Sadly all seem to be Australia. :(
Andrew Lynch
Well, as my Mom likes to say "Talk is cheap. It takes money to buy
whiskey."
Data separators require either available chips or replacements with specific
details.
I designed an FDC data separator using plain 74LSxxx parts which is great in
theory but there is no way I am going through the expense and time to build
it when there are more pressing things to do. There is no guarantee it
would work either. I am just an engineer, not a magician.
If you look closely at those old 8" SSSD 8080 CP/M machines generally they
use lots of SSI TTL and large PCBs.
Were a similar computer designed today, it would cost a LOT of money to
produce. They cost a lot then too.
A home brew SBC using PCB of those sizes would be prohibitively expensive
for most people.
As for low cost EDA tools, have you tried KiCad and FreeRouting.net? There
are links on the N8VEM website: http://groups.google.com/group/n8vem
Originally, I designed the N8VEM SBC on notebook paper by hand. Later I
recaptured the design with KiCad and used the FreeRouting.net
autorouter/manual router.
The N8VEM hardware documentation is done using KiCad/FreeRouting.net to
create schematics, PCB layout, Gerber files, drill files, BOM, netlist, etc.
KiCad is free (beer, speech) and FreeRouting.net is free (beer).
They do a great job of schematic capture, PCB layout, have fairly complete
parts library, have the ability to make custom parts, and do a great job of
both autorouting and/or manual routing of PCB traces. Total cost $0.
I doubt you'll find a 4 bit wide bit slice CPU (AMD2901) in the KiCad parts
library. That part is a bit obscure these days. However, it'd probably be
easy to do a custom part model since it is a plain 40 pin DIP with normal
IO.
The EEPROM is probably a 2816 or similar and is already in the extended
parts library.
Thanks and good luck with your project!
Andrew Lynch