Thank you for the info on 74ABTE16245. I will look for details on TI WEB
site. However my main concern with the VMEbus drivers is not their
susceptibility to input disturbances but rather the magnitude of the
ground bounce the drivers will cause when they turn on to drive the VME
backplane. There are five of the transceivers turning on simultaneously
(two each for 32-bit data and 32-bit address plus a fifth one for
control signals) when a master VMEbus cycle is executed. The
instantaneous current carried by the board ground plane and backplane
connector pins causes a significant ground bounce on the board due to
the board ground plane and connector pin inductance. This ground
disturbance is affecting the transceivers that interface to the side bus
implemented on VME connector J2, rows A and C. (The board performs a
two-way bridging function between the VMEbus and the side bus.)
I am interested in a VME-compatible backplane driver that has controlled
rise and fall times such that the maximum total di/dt is small enough to
keep ground bounce to manageable limits.
I'd appreciate any insight you might have into the matter.
John
-----Original Message-----
From: Ramzi Ammar [SMTP:[email protected]]
Sent: Friday, April 17, 1998 9:44 AM
To: O'Donnell, John; Signal Integrity Newslist
Subject: Re: [SI-LIST] : VMEbus transceivers
John, Texas Instruments offer 2 devices that were designed
specifically for
VME64 bus,
The SN74ABTE16245 and the SN74ABTE16246. Both devices have
tighter
threshold than the
normal TTL std parts, however, they are backward compatible with
TTL,
(VILMIN=1.4V vs 0.8V-TTL and VIHMAX=1.6V vs 2V-TTL). These specs
help you
eliminate the
glitches due to a wider noise margin.
regards,
Ramzi Ammar
Texas Instruments
At 05:23 PM 4/16/98 -0400, O'Donnell, John wrote:
>SI Practitioners,
>
>What is the state of the art in commercially available VMEbus
>transceivers (i.e '16245-type bus transceiver in surface mount
48-pin
>TSSOP packages)?
>
>I have a VME-hosted 6U board that provides a bridge between the
VMEbus
>and a side bus implemented on the VMEbus J2 Connector rows A
and C
>using Futurebus technology (i.e BTL transceivers). Activity on
the two
>buses is asynchronous with respect to the other bus, meaning
that the
>VME bus transceivers can turn on to drive a master transaction
to the
>VMEbus at any time during receipt of a slave transaction on the
side
>bus. The ground lift, or ground bounce produced when the VMEbus
drivers
>turn on is sufficient to cause data glitches on the local bus
outputs of
>the side bus BTL transceivers. When the VMEbus driver turn-on
happens
>to coincide with the sampling edge of the side bus data strobe
used to
>capture side bus slave data the amplitude and width of the data
glitch
>is sometimes enough to be captured in the side bus slave data
latches.
>
>The board design was based on a heritage design which used
74FCT16245
>bus transceivers to interface to the VMEbus. These devices
produced
>humongous ground bounce effects and serious data error problems
on the
>side bus. These have since been changed to 74ABT16245. This
change has
>produced a marked improvement in the side bus data integrity
but there
>are still occasional errors traceable to ground bounce effects
when the
>'ABT drivers turn on. Is there a better technology available
for driving
>a 21-slot VMEbus backplane with standard resistive terminations
such
>that the driver di/dt is restrained enough to result in a
tolerable
>ground bounce effect?
>
>Regards,
>John O'Donnell
>AYDIN Telemetry
>
>