TTL computing - test-drb@ccmp.vtda.org

9 Apr 2002

some items sorta conspired to drive cpus to multiples of 8bits.

 ASCII chars
 width of data paths internal to MOS cpus early on.
 byte wide memories, especially rom/prom/eprom

Personally I like either 18 ot 24 bits and have thought that
the PDP-8 with the right side (address portion) of the word
stretched to 18 bits or better yet 24 would be a nice machine.

24bits is majik as it's a multiple of 8.

PDP-8 addressing as 24bit   524288 word page, current and
          also there is page 0 addressing!  A field would be
          16MB.  EMA would not be needed.

Allison

-----Original Message-----
From: Ben Franchuk &lt;bfranchuk(a)jetnet.ab.ca&gt;
To: classiccmp(a)classiccmp.org &lt;classiccmp(a)classiccmp.org&gt;
Date: Wednesday, April 10, 2002 11:21 AM
Subject: Re: TTL computing

...
 Richard Erlacher wrote:

> 12-bit CPU's out there ???  Everybody knows that 12-bitters haven't
existed
...
 > since the '70's!  After all, they stop
existing on the day the last one is
...
 > shipped.  The device manufacturers stop
considering a market as viable once
...
 > the potential for 100K pieces per week per
manufacturer is no longer there.
...

True about manufacturing, but I wish one had more choice with computer
hardware/software for the PC user.I think DEC sold the PDP-8 until about
1990. Since I can't find a 12/24 bit CPU that I like I am building my
own. A 12/24 bit cpu chip could have came out around 1980  with the
8086/6800. Part of the challenge in the cpu design I am doing in FPGA is
to have it emulate (for the most part) a fictional 12/24 bit cpu in a 40
pin dip.The last thing I added was a 8 bit refresh counter for dynamic
memory and a single channel DMA for a floppy. Running at 4.9152 Mhz (
800 ns memory access, 512Kb of ram ) I hope the Squash the XT market in
1983!. :)

--
Ben Franchuk - Dawn * 12/24 bit cpu *
www.jetnet.ab.ca/users/bfranchuk/index.html