[chbot] home brew CPU

[Chris Hellyar]

Yikes.

Memories...

That's something I considered doing in the late 80's, after finishing one of my massive vero-board creations.  (an EGA video subsystem, long story. Oh the emotional scars.)

There's a chap who came from Dunedin, who's name will come to me after I send this who built a 4 bit processor using 74xx logic and entered it in a nation-wide schools science fair when I was in the sixth form.

I was entered in a team for our school and the strength of my awe at his creation on molex S100 development cards is that I can't remember what our project was but I spent hours talking to him about how he designed the clocking logic for the ALU as that was the bit I'd struggled with every time I'd put pen to paper to scribble out the blocks.  Hmm, I still have that notebook somewhere.

I also remember the the judges didn't believe he could have done it without help, but I got the impression from a long conversation with him that he definitely understood the structure and timing issues well enough to have designed it.

Cheers, Me.

For the masochists in the house, an ega video system on vero board looks like this:

http://logicalit.biz/forumimages/ega-1.jpg
http://logicalit.biz/forumimages/ega-2.jpg

Unfortunately I've robbed quite few bits off it but the major blocks are there. Three of the six video  rams are still there with latches and shift registers on the right.  (EGA is six bit / 64 colour for those not familiar with stone age colour monitors) I used an 8255A PIO to access the ram during horizontal retrace driven by a Z80. There's also a 146805E2 on there that pre-loaded the 6845 raster timing generator settings, and handled the keyboard interface and character generation.

The small daughter board held the clock generators and for some reason the reset switch.

So, what did you spend your sixth form year doing? :-)


-----Original Message-----
From: "Mark Atherton" <markaren1 at xtra.co.nz>
Sent: Monday, 15 November, 2010 22:15
To: chchrobotics at lists.linuxnut.co.nz
Subject: [chbot] home brew CPU

I was talking to one of the guys about 'real hardware' this evening, 
none of this fancy x86 stuff, I mean my first 680kHz 6800 with 256 bytes SRAM.

Anyway, the subject of the Bill Buzbee's Magic 1 came up - 
http://www.homebrewcpu.com

Shortly after moving to NZ from about 40k from where Bill lives 
(California), I found his project and helped with some of the bring 
up of the hardware via email.

So he has designed the instruction set, architecture, hardware, 
assembler and re-ported a C compiler. Not bad for a software type !

Also, just found his video on youtube - 
http://www.youtube.com/watch?v=Nv2TxiwAquM - first time I have seen him.

Also never seen MakeFair before - "an annual block party for 
tinkerers" - sounds like Wed evening at Science Alive to me.

Beware programmer who carry screwdrivers.

-Mark





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