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Re: [N8VEM-S100:660] Re: 6502 board resistor networks

Seems like there's different, perhaps competing, objectives.

One objective is to faithfully recreate legacy designs to build and experience legacy systems that might not be easily done any other way (such as finding a particular real legacy card on eBay).   My own interest is in legacy systems, but for example, finding a real legacy 6502-only board has been impossible for me, so the n8vem 6502 board is the next thing.. at least it uses a legacy design and parts.  Really, what parts cannot actually be found in some way, unless they were custom like PALs?  

Another objective is that of evolving S-100 into more modern designs and operating systems beyond, say, 1986, to beyond where it had gone during non-obsolescence eg. PC compatibility with MSDOS (aside from the CompuPro effort), or Linux.   If the intent is to produce a set of whole new designs to delve into these later systems, then these designs could easily have consistent standards across the board.   This objective is of no interest to me, but I'm sure many would get a kick of out running newer systemologies on the old S-100 standard.

Though these objectives clash if not clearly defined and left confused, they can in fact be pursued simultaneously... with a clear distinction made between a legacy offering and a new offering.

- John Singleton

lynchaj wrote:
Hi Dave,

Thanks!  I like the idea of consistent design guides however most of
our S-100 boards are legacy designs.  Most are wholly or partially
legacy designs from a multitude of sources.  For instance the S-100
6502 CPU board is a PCB implementation of Rich Leary's home brew board
used with permission.  I tried to be as close to his original design
as possible to improve the chances of a working PCB.  Similar for the
S-100 68K CPU board, I got permission from Alan Wilcox to reuse his
design.  John has a variety of home brew S-100 boards and design
elements from a mixed bag of sources. With so many different designers
it is no wonder we are seeing so much variation.  Every board has its
own story!

We do try to have some consistency across boards and reuse design
elements when possible but there is still a lot of variation.  Many of
the boards come with their own unique legacy and are particular to
their original designers.  As the designs mature, I think we can make
them more consistent through respins and tweaks but it will take
experimentation and just plain field experience to find out what
changes we can make without breaking the board.  My personal approach
is to be conservative and faithfully replicate the original design as
closely as possible.  I generally don't stray away from the original
drawings especially on the initial version.  There are just so many
variables in conversion from a home brew wire wrap design to a PCB
that broader design consistency tends to take lower priority over
basic functionality and reliability.

That being said, I think there is a lot of room for improvement as the
board designs mature.  Consistency is something we can "grow into" or
at least reduce the wild variations to something more manageable.
Thanks and have a nice day!

Andrew Lynch

On Jan 11, 10:12 pm, yoda <...@r2d2.org> wrote:
Hi Andrew

Would it be possible to have some design rules in general.  I have
seen a lot of these boards use parts that are not easily obtainable
which suggests these are copies of old boards without thought.  If
they are supposed to be pull-up resistors then in general I would
expect 1K or 4.7K be specified as they are pretty standard.  I checked
Jameco, Digikey and Mouser and they don't have 1.3 K.  I know
experienced people can interpret schematics but it tends to discourage
new people into the hobby that don't have that experience.  Also it
would be nice to do some standardization of buss interface.  I see
this board uses ls541's where most other boards use ls373's so one has
to "stock" many more parts to participate.

Just a thought