-
I did not want to change the
basic 8255 driven circuit and all the software I and
others have over the years
written for the board.
Sure if I were to
do it all over again I would probably have done it
different using perhaps a
faster Zilog PIO or an onboard fast fully dedicated Z80
(as for our ZFDC board)
or Propeller etc. The
NEC or OKI
82C55-2’s are dirt common and seem to be able to handle
anything the CPU sends
to them.
-
I want to hand lay down broad
power traces to all the boards IC’s for more even power
distribution –
particularly to the power hungry HEX displays.
-
I have inserted a trace “Keep
out Area” on the front of the board so there is no
danger of the IDE adaptors
touching a critical trace.
-
I have now switched to a “multi
regular” voltage regulator footprint.
This allows you to use either:- a
1.5Amp L7805CV, a TO-3 LM323K (3Amps), a Pololu 5 Volt
, 2.5 Amp
D24V25, or a
EzSBC.com 3A
regulator called PSU5.
-
I did bend the no new changes
rules a little and added
two 22V10 GALs. This
greatly simplifies
the board and really speeds up the port addressing and
the potential drive
select/reset issues some were having. I
realize not everybody is familiar with GAL’s. Please see
here for more
information about GALs. For those people and beginners I
will supply the
pre-programmed Lattice 22V10 GALs. The PALASM code is
shown below. Again
these GAL’s are fairly common (Jameco
#39159 for the 15ns variety).
-
Correct a potential drive A: or
B: switch circuit problem described by some.
-
I have added a wait state
circuit (0 - 8 I/O wait states) to accommodate very fast
S100 boards such as
our 80386 and 80486 boards without requiring further
generalized I/O wait
states on the CPU board for other system I/O ports.
-
People should be able to simply
switch IC’s from their old board to this new one. Only
two new GAL ICs and two
74LS373 are required.
-
Last but least I relabeled much
of the Silk Screen to be more relevant. For example
placing IC numbers above
their pin locations etc.
I have written up a description of the
board here:-
http://s100computers.com/My%20System%20Pages/IDE%20Board/My%20IDE%20Card.htm
(Bottom of the page).
This time I had 4 final productions
boards made by PCBCart (China)
before I announced it. That way I don’t have to worry
about a large batch of
boards coming back with a critical design flaw.
The picture on the web site is the final board, not a prototype.
Anyway I will do a group order for a
batch of these V3 bare
boards. Please let me know
ASAP if you would like one
or more bare boards. They will run somewhere between $14
- $16 each + shipping.
Note batches of
these boards do/will not
occur often. If
you even think you will
need such a board, now is the time.
It’s best to send me an e-mail direct
(monahan AT vitasoft DOT
org).
John Monahan