VITA 41
- VXS Backplane Introduction
VITA (VME International Trade Association) is continually striving
to maintain VME's strength in the embedded computing industry
by upgrading the technology. VITA 41 is the newest standard and
the first entry of a VME standard into switched fabric technology.
It's based on the VME64 Extensions standard with a high-speed
connector taking place of P0 in the payload slots. The switch
slots do not use the VME64X boards. The slots are made up of high-speed
connectors and a bladed power connector. The form factor and the
VME bus remain the same. Switched fabric pinouts and protocols
are defined in complimentary standards. So far, 41.1 specifies
Infiniband and 41.2 is for Rapid IO with others such as StarFabric
planned for the near future.
The most obvious
change on the VXS backplane from the VME64X backplane is the high-speed
connector on the VXS backplane. Tyco's brand name for the connector
is MultigigRT. FCI has signed on to second source the connector.
The MultigigRT is a printed circuit based, robust pinless interconnect.
The printed circuit wafers allow sequencing and electrical customization
for the VXS application. It is claimed to be capable of over 5
Gbps speeds over standard FR-4 PCB material.
The next significant
difference between the VXS backplane and a VME64X backplane is
the alignment and keying module on the VXS backplane. The backplane
contains the header side and the receptacle is on the plug-in
board. The header has the alignment pin and an IEC coding key.
The IEC coding key is the type used by CPCI backplanes and boards.
The alignment with this system is within the mechanical requirements
for all the connectors on the payload and switch boards.
Two other improvements
made are hot swap capability per VITA 41.10 and higher power allowances
for the DIN connectors per VITA 1.7. The knowledge has been out
in the industry that the 3-row and 5-row DIN connectors could
handle higher current per pin than specified in the VME64 and
VME64X standards. Extensive testing was performed by Tyco to prove
that both 3-row and 5-row DINs connectors could provide 2 amps
per pin. The results of the testing are incorporated in the VITA
1.7 standard.
Now that the
VXS differences have been introduced, it's time to look at the
backplane configuration. The payload slots have the standard 5-row
VME64X connector with the standard VME64X pinouts. P0 is now a
MultigigRT Tier 2 center module connector containing the switched
fabric links. The payload slot has one alignment and keying module
located between P0 and J1. The switch cards are populated entirely
by the MultigigRT connectors. There is not VME bussing on these
slots. There are four tier 2 MultigigRT connectors for switched
fabric links and a tier 1 MultigigRT connector for lower speed
side-band communication between switch boards. The switch board
gets +5V, VPC and ground through a four blade power connector
located at the bottom of the slot. There are two alignment and
keying modules on each switch board.
There are proposed
changes to the spec to update it to be more conducive for conduction
cooling. They will likely switch to a new Series 41 power connector
from Positronic, which will allow more room to implement the conduction
cooling. Further, they are trying to make other modifications
so that two standard PMC modules can be used on the switch card.
The VXS backplane
allows increased data plane speeds over the switched fabric. The
VME64X capability can be used for the control plane or for legacy
boards. VXS is a intermediate step between VME64 world and the
switched fabric world where the user may dance between the two.
Melissa Heckman
Electrical Engineer
Bustronic
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