Re: [SI-LIST] : VMEbus transceivers

Ramzi Ammar (r-ammar@ti.com)
Fri, 17 Apr 1998 08:44:15 -0500

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
>
>