Last April's newsletter presented an overview of PICMG's latest effort, the PICMG 3.0 Advanced TCA Specification. It has been voted on by the subcommittee members and is in negative ballot review. It is expected the specification will go to the Executive Committee for approval at the Bus & Board Conference in January. Now that the specification is completed it is a good time to look at the mechanical aspects of the backplane in some depth.

The backplane is approximately 5U tall to allow for the rear transistion module interface. If the rear transition module interface is added to the backplane it is 8U tall. The slot pitch is 1.2" so a 14 slot backplane will fit in a 19" rack. The specification allows for a 16 slot backplane, which fits into a 23" chassis.

The backplane is broken up into zones. Zone 1 contains the power connector. Zone 2 is made up of the signal connectors carrying the base interface, clocks, update channel interface and the fabric interface. The base interface uses an Ethernet Dual Star topology. Sub-specifications PICMG 3.1 (Ethernet), 3.2 (Infiniband), 3.3 (StarFabric), and 3.4 (PCI Express) determine the fabric used over the fabric interface. Zone 3 is the rear transition module area. The power connector was specially designed by Positronic Industries for the PICMG 3.0 application. It is a 34-pin press fit connector, with two redundant 48V DC feeds. Signals on the power connector are tip and ring, redundant ringing generators, hardware address bits and redundant IPMB busses. The signal connectors in Zone 2 are ZD connectors manufactured by ERNI and Tyco. Horizontally the columns have 5 differential pairs and vertically there are 10 rows. The ZD connector is specifically designed for high speed differential signaling, and is capable of speeds up to 5 Gbps.

At the top of the backplane above Zone 2, there is provision for an alignment key to enable proper insertion of the front card. If a rear transition module is called for, the gross alignment key is inserted on the rear of the backplane.

To see Bustronic's ATCA backplane developments, including some simulation info, visit http://www.bustronic.com/pdf/atca_DS.pdf

Melissa Heckman
Electrical Engineer