[SI-LIST] Re: quenching ugly spikes?
- From: "Grist, Robert" <RGrist@xxxxxxxxxxxx>
- To: <hencox@xxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Fri, 28 Oct 2005 08:22:12 -0400
I would first start with your scope probe. How long is the ground wire? =
It needs to be as short as possible, perhaps even shorter than that. If =
possible, try an active fet probe. Scope probe ground inductance has =
caused many a person to go chasing their tale.
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Henrik Gild
Sent: Thursday, October 27, 2005 5:14 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] quenching ugly spikes?
Hi!
As a hobby I'm designing an Ethernet/USB board for those Atari computer
enthusiasts who are still active. My board sits on top of an accelerator
board containing an MC68060 and a couple of CPLDs, connecting to my =
board
through two 2.54mm (0.100") 2x25 pin connectors (one for data lines and =
one
for address/control). My problem is that I get really ugly signals from =
the
accelerator board. They are supposed to be 3.3V signals but I see spikes =
all
the way up to 6V on the address lines and the data lines start off with =
a
small 2V top, then down to -1V and finally up to a 5.5V spike before
settling at 3.3V after a total of 18ns. I assume that these symptoms are
caused by two things:
1) There are no series resistors on any lines on the accelerator board, =
and
the data lines are as long as 22cm (about 8.5"). The rise times are
somewhere in the 2-3ns region, so I suppose the lack of series =
termination
is not a good thing. I have series resistors on my board and when my =
board
drives the signals they look much nicer.
2) There are only two ground pins at each end of both connectors, in =
total
four per connector. The lack of nearby ground pins for the data and =
address
lines isn't good either?
What do you think I can do about this? I've tried terminating using =
diodes
(though only 1N4148) but that didn't change anything. I'm thinking of =
using
chokes on the lines. Could that be a good solution?
Both my board and the accelerator board are four layer boards with =
dedicated=20
ground and power layers.
I hope you can help me out! :)
Thanks!
/Henrik Gild=E5
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List FAQ wiki page is located at:
http://si-list.org/wiki/wiki.pl?Si-List_FAQ
List technical documents are available at:
http://www.si-list.org
List archives are viewable at: =20
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
=20
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List FAQ wiki page is located at:
http://si-list.org/wiki/wiki.pl?Si-List_FAQ
List technical documents are available at:
http://www.si-list.org
List archives are viewable at:
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
