22 Jul
2008
22 Jul
'08
10:18 p.m.
-----Original Message-----
From: Andrew Lynch [mailto:lynchaj at yahoo.com]
Sent: Sunday, July 20, 2008 5:17 PM
To: 'cctalk at classiccmp.org'
Subject: Experience with ECB bus?
Hi
I am designing an ECB bus backplane for my N8VEM SBC project and am
looking for some peer review prior to going to manufacturing of these
PCBs. The N8VEM SBC seems to be working out alright. About a half dozen
people have successfully built the SBC so now it is time to start thinking
about peripheral expansion.
Although the N8VEM SBC uses the ECB bus for expansion, I have not ever
used ECB bus machines as they are common in Europe but extremely rare in
the US. I have made an ECB bus backplane prototype using prototype boards
and it works well enough so I think the basic concept is sound.
However, I would like to make this ECB backplane as common and general as
possible so other hobbyists can use it not just N8VEM SBC builders. I
would really like to avoid any inadvertent N8VEM unique extensions.
If you have experience with ECB bus based machines, I would like to hear
your comments and suggestions.
So far, the ECB bus backplane has six DIN 41612 connectors. All 96 pins
are routed. Pins for IEI/IEO have jumper pads per connector to allow
usage of Zilog peripheral interrupt priority scheme. The backplane has
its own Vcc and Gnd, including a power switch and LED power indicator.
The PCB is 2 layer to keep costs low. Each side has a ground fill zone
for a low impedance ground. I will be using the double thick PCB material
(3.2 mm) for rigidity and the double weight copper trace for low
impedance.
Vcc and ground traces are triple wide (51 mils) minimum and also routed on
both the component and copper sides of the board. The rest of the traces
are the usual 17 mils wide.
After I order some of these backplanes, I will make them available in a
similar fashion as the N8VEM SBC. The PCBs will be available for $20 each
plus shipping. The builder will have to source the rest of the parts.
If you are interested in helping or have questions, please review the PCB
backplane design at:
http://groups.google.com/group/n8vem/files?&sort=rdate
There are two recently uploaded PDF files containing the schematic and the
PCB layout.
Thanks in advance for any *constructive* feedback. Have a nice day!
Andrew Lynch
[AJL>]
Hi All,
Well, it seems like no one has experience with the ECB bus which rather
surprises me as I am sure there are many people on this list from Europe
and/or the UK.
If there is anyone with PCB design experience who could review my design, I
would appreciate it. The PCB will run at around 4 MHz and some may take it
as high as 10 MHz. The N8VEM SBC runs at 4 MHz so that is my desired
operating speed but I cannot rule out people modifying their SBCs to run
faster.
Specifically, I am concerned about using the extensive ground fill zones and
also the ground and VCC traces are on both the copper and component sides of
the PCB. Even though the PCB is small, am I causing potential ground loops
with excessive traces?
I am trying very hard to make low impedance paths to ground and also allow
sufficient low impedance current carrying capacity for VCC. I suspect the
fully loaded ECB bus would draw maybe an amp or two on the VCC rail. The
worst case for the N8VEM SBC is about 500 mA or so and much less if CMOS
components are used.
If anyone could help, I would much appreciate it. The ECB is a rather
uncommon bus in the US but was used extensively in home brew computer
projects in Europe. The ECB bus is a natural extension of the Z80 and is
very nice to work with not to mention extremely affordable compared to S-100
or STD since you can make your own inexpensive peripherals with a cheap
prototype board ($5) and a DIN 41612 connector ($3).
My N8VEM SBC project uses the ECB bus and will plug into the ECB backplane
when it is available. I will be selling the ECB backplane connector PCBs to
anyone interested in the same manner as the SBC PCBs are available. You can
see additional details at the N8VEM website:
http://groups.google.com/group/n8vem
Thanks and have a nice day!
Andrew Lynch