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RE: [N8VEM-S100:1029] A new S-100 6502 CPU Board

Hi!  At this point since the W65C816S is an 8/18 bit chip I would suggest a
16 bit S-100 CPU board built around it.  Then the board could use the
S-100/IEEE-696 16 bit extensions and be purely 16 bit rather than tweaking
the S-100 6502 CPU V2 board which is a fundamentally 8 bit CPU design.  The
W65C816S plus a few external support chips basically form a 16 bit core CPU
that should drop in place to a similar infrastructure as the S-100 8086 CPU
board or S-100 68K CPU board.

One thing we could do with the existing S-100 6502 CPU V2 board design is
modify it to be switchable between 6502, 6809, and 6802 CPUs.  It takes only
a little extra logic and PCB space to support all three CPUs since they are
so similar in design.  Take a look at the 6x0x host processor project on the
N8VEM wiki.  It is marginally associated with the ECB side but is really its
own separate entity.

However, at the moment we have a lot of irons in the fire with several board
designs in work.  I'd suggest doing some research on what would be a good
W65C816S core CPU and how to splice it into an existing 16 bit S-100 CPU
board.  For sure it would need at least 16 bit data and address bus logic
and buffers.  Probably some means to communicate with 8 bit IO boards, etc.
This certainly is doable but will take some investigation and probably a
prototype board or two.

It would be a good project once the S-100 80386 CPU & DRAM boards, S-100
VGA, MC68040 SBC, etc are working.  I am keeping a "rainy day" queue of
projects like the S-100 VDP, S-100 uPD7220 GDC, S-100 SCSI-1, S-100 ECB
bridge some others.  Actually a page on the wiki would be handy to help
remember neat S-100 board projects for we are so heavily loaded.  Any

Thanks and have a nice day!

Andrew Lynch

> -----Original Message-----
> From: n8vem...@googlegroups.com [mailto:n8vem-
> s1...@googlegroups.com] On Behalf Of Ian May
> Sent: Tuesday, August 07, 2012 4:20 AM
> To: n8vem...@googlegroups.com
> Subject: Re: [N8VEM-S100:1029] A new S-100 6502 CPU Board
> Hi John, you are probably too far down the design path for the new board
> change CPU now. What I was suggesting was using the W65C816S instead of
> a 6502. At reset the W65C816S behaves exactly like a 6502 but when you
> switch to native mode it turns into a 24 bit addressing machine with 16
> index registers and accumulator. The program counter is still 16 bits, the
> 8 address bits come from the program bank register. To get beyond the
> bottom 64K there are JMP and JSR instructions that have 24 bit address
> operands (much like far calls on an 8086). There is a data bank register
> generates the top 8 address bits for data instructions.
> Jameco has them for $7.95 versus $6.95 for the W65C02 so the price
> difference isn't much. Unfortunately the W65C816S is not pin compatible
> with the 6502 so you can't drop it in later. If you were to use the
> you would have a board that behaves exactly like a
> 6502 but has the ability to transform into a machine capable of natively
> generating 24 bit addressing without messing around with external page
> registers.
> In hindsight I should have mentioned the W65C816S when you announced
> the first 6502 S100 board.
> Cheers,
> Ian.