homemade computer for fun and experience...

From: jpero_at_cgocable.net <(jpero_at_cgocable.net)>
Date: Sun Apr 4 20:14:29 1999

Date sent: Sat, 3 Apr 1999 9:25:05 -0500
Send reply to: classiccmp_at_u.washington.edu
From: CLASSICCMP_at_trailing-edge.com
To: "Discussion re-collecting of classic computers" <classiccmp_at_u.washington.edu>
Subject: RE: homemade computer for fun and experience...
Originally to: classiccmp_at_u.WASHINGTON.EDU

Viewing Tim's splattering on the wall...

> Why restrict yourself to PC-clone keyboards? May as well just put a
Snip!

Because, as I have traced around countless motherboards of all
kinds and found this is far easier to cobble up one using keyboard,
KB controller stolen from old motherboard, than trying to design
and build a parallel KB or design an i/o and needed codes for
terminal. I have heard horror stories from some who did the parallel
kbs and they're no longer made. I could be mistaken.
 
> If I were you, I wouldn't restrict myself to what's in the junk box.

Hold on, doing it is real education and it's what makes me so alive
about it. Done that on a appox 10 TTL chipsets with few analog
sensors thrown in. In theory this works and manually stepped thru
works 100% but has bugs in the sensor/analog threhold circuit
area. 5 sensors (1 to step counter that feeds address to SRAM,
group of 4 for data) 16 x 4bit SRAM with a button (WE) to store all
64bits of data in one pass by master media under sensors, nyble
of data from sensors and SRAM into AND circuit to trigger counter
that displays # of matches. No syncing circuits, media to be
scanned is sync in themselves.

Still have that original project materials and the prototypes.
Did that in final year of H.S. of '93 and despite it's bugs got high
marks.

Back to VGA card idea, problem is: has to init the that stupid thing
and worse thing as a first timer to face is to emulate the ISA. That
is wayyy later in series of hazy future projects. Using SRAM for
first time is easier to do as I had done in HS. Putting on i/o ports
like parallel and serial is next in number of adds ons as I progress
in that project. Driving the terminal is both bios, and hardware
driven with most of it in software for it. I'm not yet at this point.

So, starter machine:

AT keyboard + KB controller pulled from old MB, 6845 4K text
video driving TTL monitor, ram and bios after I get the firmware done
and put into bios. That will pave way for i/o and FDC, finally CPM,
then HDC. Onwards... who knows!

Based on Z80 cpu? Should I put in a programmable timer IC to
lessen use of "looping" that some s/w used to pace certain things?

CPU, ram/rom, ttl glue logic, few associated LSI IC's like i/o ic and
6845 w/ 4K seperate ram.

What ideally I like this way is to push data and instructions at
items instead of "over-handshaking by s/w disease" before
signicent results appears?
That makes me think of winmodems which I don't like.

6801, 6809, parts of 386dx, Z80, 6502 or suitable CPU that have
freely available docs on websites? My major is $ and space is
lacking for keeping books. But I have so MUCH silicon and active
brain.

Wizard
Received on Sun Apr 04 1999 - 20:14:29 BST

This archive was generated by hypermail 2.3.0 : Fri Oct 10 2014 - 23:31:39 BST