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RE: [N8VEM-S100:494] Re: S-100 6502 CPU poll

One of the nice things about the S-100 bus is that you can isolate a
hardware problem  quickly and easily if you separate functions to individual
boards. So a separate video board, a separate I/O board, a separate RAM
board, separate FDC board and separate HDISK board etc.    I have the luxury
of having two systems. My main box 22 slots, and a "test" system 10 slots.
If something goes wrong in the main system I simply trim the system down to
the minimum and add one board at a time. Has got me out of many a
frustrating situation.  While the above is probably not for everybody, you
can pick up old static RAM boards, I/O boards etc. for next to nothing on
eBay and have a simple fall back plan ready for when Murphy strikes.   BTW,
its really good to do all this BEFORE your system crashes. You know
beforehand what works. 

This is a huge advantage of the S100 system often not realized.   For most
people there are plenty of empty slots it really makes sense to isolate
functions one per board.  The downside is the cost of each board and a few
extra V regulators and support chips.  At $20-30 per board that Andrew can
get, it's well worth it.  

There is (in my opinion) only one exception to this approach and that is
placing a boot PROM on a CPU board.  In this case not only do you gain a
slight access time advantage (less wait states) but that PROM is invisible
if you have a second/different CPU on the bus.  You don?t want for example a
Z80 PROM sticking a "hole" in the 1MB address space of the 8086. Likewise an
8086 PROM in the 80286 address space.
There at phantom lime workarounds but they can get sloppy and take up board
real estate.

So... per my last e-mail, yes I would recommend an on-board EPROM (only) on
the 6502. I would not recommend for example a separate Console IO port,
video port etc.


John Monahan Ph.D

-----Original Message-----
From: n8vem...@googlegroups.com [mailto:n8vem...@googlegroups.com] On
Behalf Of lynchaj
Sent: Friday, November 25, 2011 7:12 AM
To: N8VEM-S100
Subject: [N8VEM-S100:494] Re: S-100 6502 CPU poll


Another point to consider is the potential for onboard SRAM and/or IO and
the TMI multiple bus master circuitry is itself highly specialized.  Many,
if not most, S-100 builders will not use any of those.  If you already have
an existing S-100 bus system and are willing to operate it with a dedicated
S-100 6502 CPU as sole bus master and use other boards with RAM and IO then
the V2 modifications are basically not useful to you.  In fact, they may
*cause* more problems than they fix.

S-100/IEEE-696 systems *tend* to be "one function per board" and as a result
highly integrated boards tend to be problematic.  Maybe John Monahan would
further elaborate on the  approach of "one function per board" design
philosophy.  We've held it fairly well with the boards we have made so far.

Thanks and have a nice day!

Andrew Lynch

On Nov 25, 2:19 am, "Leon Byles" <le...@swiftdsl.com.au> wrote:
> Hi Andrew,
> I would be interested in getting a 6502 board now if you can get 
> enough takers for a production run.
> It looks like a nice board to play with.
> Leon  Byles