Author: Manfred Schmitz, Chief Technical Officer, MEN Mikro Elektronik
Just like parallel CompactPCI, CompactPCI Serial defines two standard board sizes: single and double Eurocards. The smaller single Eurocard format (100 x 160 mm, 3U) is particularly suited for compact and mobile applications. In the fields of servers, telecommunications and measurement, larger card formats (233 x 160 mm, 6U) may even be an advantage, since the electronic components need more space and can draw more power.
The two formats are electrically and mechanically compatible. This means that you can insert 3U boards also into 6U systems without restrictions. The connector types and even the pin assignment are identical. The only difference is that for 6U boards an optional connector (P0) was added to amplify power supply and to provide additional Ethernet channels as an infrastructure bus for server applications.
However, 3U boards with CompactPCI Serial are not inserted at the bottom, as for (parallel) CompactPCI, but at the top, as was the case for the older VMEbus standard. This has two reasons. On the one hand, it is necessary to amplify the power supply for 6U boards. 3U boards are supplied via the P1 connector. For 6U, this connector needs to be extended. For EMC reasons and in order not to influence data transfer on the serial interconnects, the power supply connections have as large a distance as possible to the critical signal paths. It is only logical to place the additional P0 connector directly next to P1, i.e. below P1. This makes the board grow towards the bottom. It is important to note that P0 is the only electrical extension of 6U boards compared to 3U boards. All features of CompactPCI Serial such as 8 PCI Express links, 8 full-mesh Ethernet, 8 SATA and 8 USB interfaces are available in 3U systems just as in 6U systems. The second reason is the simple build-up of hybrid boards. CompactPCI Serial also describes this kind of board. The upper area of a 6U board accommodates the new AirMax connectors, while the lower area uses the common 2-mm connectors of (parallel) CompactPCI in their standard positions.
An essential feature of CompactPCI Serial – PICMG CPCI-S.0 – is its compatibility to parallel CompactPCI – PICMG 2.0. Making 3U boards compatible with 6U boards and at the same time creating the possibility to implement 6U hybrid boards, is an important prerequisite for a smooth transition from existing solutions to modern serial buses.