Re: 6502 board resistor networks

[lynchaj <lyn...@yahoo.com>]

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
>
> On Jan 11, 6:50 pm, "Andrew Lynch" <LYN...@YAHOO.COM> wrote:
>
>
>
> > Hi Kipp!  The 1.3K ohm resistors are all pull up resistors and have a broad
> > tolerance.
>
> > Almost certainly the 1.2K ohm resistors will work just fine.
>
> > Thanks and have a nice day!
>
> > Andrew Lynch
>
> > > -----Original Message-----
> > > From: n8vem...@googlegroups.com [mailto:n8vem-
> > > s1...@googlegroups.com] On Behalf Of kyeakel
> > > Sent: Wednesday, January 11, 2012 10:44 AM
> > > To: N8VEM-S100
> > > Subject: [N8VEM-S100:655] 6502 board resistor networks
>
> > > I couldn't find 1.3k ohm resistor networks. I have 1.2k networks, any
> > issue
> > > with using them?
> > > Kipp- Hide quoted text -
>
> - Show quoted text -