Author: Manfred Schmitz, CTO MEN Mikro Elektronik
CompactPCI Serial, PICMG CPCI-S.0, uses so-called AirMax connectors to link the plug-in card to the backplane. These connectors were chosen for their high pin density, their excellent transmission behavior with high signal frequencies, and for their mechanical robustness. They are completely compatible with the IEEE 1101 standard, which is the mechanical basis of parallel CompactPCI and, consequently, also CompactPCI Serial.
The connector has segments. This means that depending on the board's function, not all connector segments are assembled. Especially connectors P2, P3, P4 and P5 are specified for user-defined I/O on peripheral cards and offer a total of 360 pins, 120 pins of which are normally defined as GND. If a rear I/O board is connected at the rear of the backplane, and the I/O functions are customized, the pin-out must correspond 100% with the front board. If you plug a card with a customized signal assignment into a wrong slot, the card could be damaged.
The layout of the boards and backplane summarizes P2 and P3 as well as P4 and P5 as one hole-pattern block. As long as the block is completely assembled, you can populate it with any desired AirMax connectors. There are AirMax connectors with 6, 8 and 10 rows. The connectors are mechanically coded. A plug connector with 8 rows, for instance, cannot be plugged into a receptacle with only 6 rows.
The standard prescribes that block P2-P3 may be populated by two 8-row connectors, but also with one 6- and one 10-row connector. This makes for three possible P2-P3 configurations: 6-10, 8-8, 10-6. Block P4-P5 can be populated by 8-6 or 6-8. This makes a total of six different connector arrangements for customized I/O boards. The corresponding backplane must be populated by the receptacles matching the I/O board but uses the standard layout.
This coding option is another alternative to those already provided by IEEE 1101. The connectors are assembled correspondingly when the board and backplane are manufactured, so that the user cannot make any mistakes.
CompactPCI Serial is based on a carefully defined specification that leaves nothing to chance. At the same time it offers the user more options for customized signal routing than any other standard before that.