Re: [N8VEM-S100:664] 6502 board resistor networks

[Neil Breeden <nbre...@comcast.net>]

This is the kind of discussion that should be captured, cleaned up and placed in the wiki for the newbies / those without EE knowledge. Part of the N8 effort is to help people gain knowledge and grow skills.

-N

On Jan 12, 2012, at 10:26 AM, yoda wrote:

> I agree with your statements - I think there can be some relaxation of
> some things.  Some parts
> are difficult to come by now and I would hate to discourage new people
> from participating because of
> that - so there has to be a balance.  Not all participants are
> electrical engineer types so it can be
> frustrating to them not knowing where they can substitute.
> 
> On Jan 12, 10:59 am, "j....@cimmeri.com" <j....@cimmeri.com> wrote:
>> 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 <y....@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
>> 
>>>> Dave