CompactPCI Serial - The Next Generation CompactPCI

Rear I/O with 6U CompactPCI® Serial

2010-11-06, Manfred Schmitz

CPCI Serial in 6U w/ user-definable rear I/O area

Rear I/O in the 6U area is very important for many applications. Telecom applications, for example, only allow front I/O for service purposes. The reason for the use of modular systems based on plug-in cards is actually the extremely short time that is needed to exchange boards in the case of service. Thanks to the hot-plug capability of CompactPCI® Serial (CPCI-S.0), you don't even have to switch off the power to exchange a board. Many connections at the front, which would have to be removed before exchange, could completely undo this advantage. The solution is rear I/O.

In measuring technology there is yet another motivation for rear I/O. A board with an analog front end often needs an adaptation for measuring values that is different for every application. You can very well accommodate line drivers on a tailor-made rear I/O adapter. This leaves the front for convenient status displays.
Rear I/O technology also incorporates two major difficulties. In common CompactPCI® systems, all signals must be led from the front to the backplane. The backplane's connectors route the signals on to the rear I/O adapter. With (parallel) CompactPCI® the rear I/O and also the PCI bus signals are fixed to 2-mm connectors. These are not well suited to support the high bandwidths of digital communication or to handle highly sensitive signals in the field of measurement engineering.

This is why CompactPCI® Serial completely does without a definition of the rear I/O connector and even leaves out the backplane in this area. The individual connector of the front board directly meets the corresponding connector of the rear I/O board.

This approach has only benefits: Having nothing to do with rear I/O, the backplane becomes smaller and less expensive. As not all the slots may use rear I/O, because they don't need it, no connectors are reserved for rear I/O at all. While there is still a discussion in the VPX area on how to support optical interfaces, CPCI-S.0 offers a trouble-free way to make this possible. The front board can directly meet any desired optical connector of the rear I/O card. The same goes for sensitive signals in the area of measurement engineering. Special connectors with a high signal-to-noise ratio of the front board can directly contact the rear I/O board.

This makes the concept for 6U rear I/O of CompactPCI® Serial equally suited for applications like optical data transmission or the transmission of highly sensitive signals. In the same way you might as well employ common 2-mm connectors, for instance for hybrid boards. The rear I/O connector then leads the signals of the parallel PCI bus to the rear I/O adapter. In this special case, the rear I/O adapter is simply a common CompactPCI® backplane.

CPCI-S.0 on the one hand offers a very high degree of interoperability by only a few options, while on the other hand putting hardly any limits to individuality.

CompactPCI® Serial in 6U with user-definable rear I/O area

Manfred Schmitz, Technical Director MEN Mikro Elektronik

Rear I/O with 6U CompactPCI® Serial

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