Rumor has it that Pete Turnbull may have mentioned these words:
>On Sep 15, 14:42, Roger Merchberger wrote:
[snip]
>(It can be done
> > easily without the switches -- I could use a jumper block without
> > heartburn, but the switches would look neater, and wouldn't have the
>chance
> > for floating inputs/outputs...)
>
>In other words, this:
[snip gfx of my idear...]
Yup.
>Wouldn't this be easier and do the same thing?
[snip better idear...]
Probably. I did mention that I was primarily a softee-ware guy -- and when
dealing with chips I have a tendency to think of them *as software* --
like: if you try to write to a ROM, what happens? Nothing. (duh...) I
looked at the chip specs for the demux, and you have inputs & outputs... In
my mind (at first), your suggestion was "ramming 5V down an output port"
and sometimes I have to stop & think that "those ports are just a bunch of
gates jammed together on a chip to serve one purpose" and doing stuff like
that is not a "Bad Thing (TM)." :-)
The design continues... :-)
>I've just seen Tony's reply, and his suggestion using a MUX would have been
>my next suggestion too. It's also easier to extend to more address bits
>(fewer switches required).
My board isn't a "complete" board -- it's to be designed to make
experimenting much easier by having flexible on-board address decoding, and
(at least for my purposes) I want "one address per switch", so I'm not sure
if the MUX suggestion is what I want. As of right now (but I'm still
researching CoCo memory maps) I'm looking to have an 8K ROM socket at the
"normal" location ($C000-DFFF) w/jumper as to whether or not it will
auto-start (jumpering the Cart signal to the Q line) and I'm looking at
having the address decoding for my I/O ports at $FF50-3 & $FF60-3, but if I
want *just* $FF51 & $FF53 to be decoded & $FF50 & $FF52 to be ignored, I
want to be able to switch them individually.
(Originally, my design was just going to have 1 address decoded from each
"bank", but then I realized that if I wanted to interface "most anything"
like a PIA, UART or a FDC that it wouldn't work.)
For anyone here who does their own hardware designing, what software do you
use? I've tried "Protel 99 SE" and CircuitMaker 6 (student version) -- and
a few others, and I must say that I'm not keen on most anything I've tried
compared to "good ol' AutoCad".
Anyway, an updated (and large) picture (of both sides of traces - red is
solder-side, lt. blue is component side) of the board is here:
http://www.30below.com/~zmerch/xpndr1/CoCoBoard.gif (118k, 16color, looks
like crap, but is smaller than the jpg)
http://www.30below.com/~zmerch/xpndr1/CoCoBoard.jpg (180k, 24bit color,
looks decent but is a slow download for modem users)
http://www.30below.com/~zmerch/xpndr1/CoCoBoard.dwg (85k, but only viewable
if you have AutoCad .dwg compatible software...)
As the board I started out with was just a bare board, I seriously doubt
that I'd get into any type of copyright trouble by the time this thing gets
to press; everything you see in the pix stemmed from my own brain...
Oh, I've found a really good site to purchase all manners of circuit board
"stuff" w/really good prices, too:
http://www.web-tronics.com/printed-circuit-board-supplies.html
As always, Thanks everybody for all the help I've received so far...
Roger "Merch" Merchberger
Received on Sat Sep 22 2001 - 12:11:07 BST
