[Coco] What would a CoCo successor have to have as a minimum?

[gene heskett]

On Tuesday, November 23, 2010 12:34:59 pm Steve Bjork did opine:

> I programmed on both the 68000 and 65816 back in day as home console
> game designer.  I will tell you that 68000 was a dream to program on,
> the 65816 was a nightmare.  Just as the 6502 had real problems dealing
> with the 8-bit boundary (every 256 bytes) the 65816 has the same problem
> with 16-bit boundary (every 64k).
 
I take it that this seemed to be a reasonable trade-off since at the time, 
the Z-80 also suffered from this limit.  I wrote a broadcast ATS to run on 
the Z-80, and the result by the time my code was needing an 8k byte eprom 
to hold, was probably 20% of the overall code devoted to maintaining multi 
page jumps.  Frankly, it was the biggest PIMA code I ever wrote, and only 
used the Z-80 because that was what was on the Mirco-Professor development 
board of the day and relatively in-expensive.  I could have done it in half 
(or even less) the code on an RCA 1802.

> The design of 6502 was in the day when CPU were expensive to design and
> make. Just removing one logic gate on the CPU made a real difference in
> cost.  So the designers of the 6502 save logic gates by making every
> register 8-bits when they could.  (Even the x and y memory pointers were
> just 8-bits.)

Just one of the reasons I always considered both it and the Z-80 as being 
drain bamaged cpu's, with no real comparison to the 1802-4-5, or the even 
newer 6809.

Now definitely off topic:

My personal 'vintage cpu' list only has 2 entries, 6x09, and 1802-4-5.  The 
unusual architecture of the 1802 family was, AFAIAC, 2 generations ahead of 
its time, and its a crying shame that its internal clocking, never modified 
in 2nd generation chips, meant it took 8 clocks for one machine cycle, at a 
1 mhz clock.  I found it more than fast enough for what I was doing at the 
time, circa 1978.

I have often wondered if a fpga image of the 1802 that matches clock and 
machine was ever developed, but have no clue how to do a poodle search to 
find out.  Ahh, yes, and no.  There was such a project on the retro contest 
site,

 <http://retrochallenge.net/RC2010/index.html>

2nd place winner this year, but the actual link that should reach it is 
down, NDI why.  A takedown notice from whoever owns rca?
It was done in an fpga.  There is also an emulation called emma2, how good 
I have no idea.  I'd druther have the real thing in an fpga.  The  the code 
I still have a paper copy of, and a broadcast cart image of, would run, 
provided I had the hardware for all the I/O it used.


> Even the great and power Woz pick the 6502 for his Apple computer not
> because he liked the design of the 6502.  The chip was so cheap that Woz
> got one for free from the supplier and built a computer around it.
> 
> Yes, the 65816 was a step forward and loved by those that only
> programmed 6502.  But for those with a more diverse CPU background saw
> the chip as a way to keep the worst design parts 6502 alive in the world
> of 16 and 32 bit computing.
> 
> Don't get me wrong,  there was a place for the 6502.  It was a good
> choice for small little devices that did not have much in the ram or
> hardware, like the Atari 2600.  I don't think that game system would
> have done as well if you used a CPU that cost more in both $$$ and code
> space.
> 
> Steve Bjork
> 
> On 11/22/2010 11:32 PM, Little John wrote:
> > Just wanted to toss in a bit about extending the CPU...
> > William Mensch extended the 6502 to 16 bits with his 65816. It could
> > still run as a 6502, but also had it's 16-bit mode with a 16-Megabyte
> > address space. There was also a version called the 65802 which was a
> > 65816 that could be plugged directly in place of a 6502 (I don't think
> > it supported the extra memory though). Might something similar not be
> > possible with the 6809?
> > -JohnT-
> 
> --
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-- 
Cheers, Gene
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-Ed Howdershelt (Author)
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		-- Bernie Greenberg.