Although the MicroTCA specification agreed in July 2006 was developed with particular focus on the telecommunications market, there has also been very strong interest in MicroTCA in other market sectors from the outset, particularly in industry. Yet some requirements here differ fundamentally from those of the telecoms market. Industry does not demand 99.999% failure safety, so full redundancy is not necessary. Many of the system and shelf management functions defined in the MicroTCA standard are likewise surplus to requirements. For this reason, simplified and cost-optimised MicroTCA-based solutions have been developed for industrial applications. However, not every user is ready to take the major step of an all-out change to this new technology. Schroff has therefore developed a hybrid system (Fig. 1) that combines trusted technologies such as VMEbus or CompactPCI with MicroTCA in a single system.

It has been shown that MicroTCA fulfils the necessary conditions for successful use in industrial applications. Its high degree of flexibility allows the most diverse system concepts to be realised, from a very small, minimally equipped two-slot chassis to a fully redundant, telemonitored system - based on one platform and thus using standardised components. The investment is scaled to the required functions. Future-proof protocols offer sufficient performance reserves and data throughput for the next generation of processors. It is also certain that the bus driver building blocks will be available on the market for the long term. A wide range of available AdvancedMC modules are now ready to go into production as off-the-shelf components, e.g. CPU boards, hard disk modules, digital signal processors and gigabit Ethernet switches.

Many users would like to benefit from the advantages of MicroTCA but are not ready to make the all-out changeover from their existing technology. The costs of migrating existing solutions to a new platform are high, and MicroTCA know-how is not yet complete. Firms in this situation can now opt for the Schroff MicroTCA hybrid system (Fig. 1), which allows them to work with two technologies in parallel. The latest AdvancedMC processor modules can thus be easily harnessed to the large ECO system on existing CompactPCI or PMC I/O solutions for applications in industry.

The connection between existing VME or CompactPCI boards (19" plug-in modules) and MicroTCA naturally involves both mechanical and electrical implementation. MicroTCA mechanics is basically a development of the 19" technology that has been proven and tested for decades. A MicroTCA system is based on the same 19" subracks as a VME or CompactPCI system; only the internal construction (board cage) is different. MicroTCA has a different form factor, i.e. different board dimensions, and therefore requires special guide rails and front panels. The new hybrid subrack is built as a standard 19" subrack in 3 U that is equipped on one side with existing 19" components. A MicroTCA board cage is built into the other side of the subrack, into which AdvancedMC single modules can be inserted. This MicroTCA board cage can be positioned left, right or central in the system and can have any desired width. The entire system is built of existing standard components. Only the separating wall between the MicroTCA board cage and the rest of the 19" subrack is new. The board cage is EMC shielded in itself and is bolted to the 19" subrack.

Classic 19" systems almost all have a board depth of 160 mm, but MicroTCA defines a board depth of approx. 180 mm. In order that a single plane can be created on the front for MicroTCA and CompactPCI, PXI or VME, the backplanes in the system must be mounted on different planes. It is also possible, however, as with the hybrid subrack, to mount the backplanes on the same plane and the MicroTCA part will still seal flush with the system front (Fig. 2). This is ensured by the IEE horizontal rail, that is pulled further outwards for the extractor handles of the 19" front panels.

The electrical connection via a common, through-connected backplane is somewhat more complex than the mechanical link. After all, two different worlds are to be joined: on the one side MicroTCA with serial data transmission (e.g. with serial ATA, PCIe or other protocols) and on the other side a parallel bus (e.g. CompactPCI or VMEbus).

The simplest and most flexible method of joining the two worlds is to use two isolated backplanes - a MicroTCA backplane and a CompactPCI, PXI or VME backplane (Fig. 3). The connection between the buses is made in this case via an AdvancedMC module that has an MMC (module management controller) and is thus tied into the MicroTCA management concept.

The board has a PCIe data interface and provides PCIe on a front panel cable. In the 19" area a special board is used in turn to receive the PCIe via a front panel connector and implement CompactPCI, PXI or VME on the parallel bus. With minor modifications this solution can be very easily adapted to standard products; various CompactPCI, PXI, VME and MicroTCA backplanes can be easily swapped. The flexibility of this solution is very high.

The disadvantage, however, is that two slots must be sacrificed in order to provide MicroTCA on the parallel bus. It is thus also possible, once the application is set up and the backplane for the project is defined, to develop a monolithic backplane that contains both the MicroTCA part and the parallel PCI or VME bus. In such a solution, the backplanes of both mechanics are brought to one plane, so that a monolithic backplane can be used. The electrical connection between MicroTCA and the parallel bus can be effected in various ways. Firstly it is still possible to link the two buses via an AdvancedMC- module and a 19" board via front cables. A further option is a mezzanine board on the rear of the backplane that behaves towards the MCH like an AdvancedMC module and provides PCIe on PCI or VME. This logic can also be integrated directly onto the backplane.

MicroTCA also defines shelf and carrier management systems that are not available as such in CompactPCI. An MMC (module management controller) sits on every AdvancedMC module. The MMCs are controlled by the MCMC (MicroTCA carrier management controller) on the MCH. This ensures that the AdvancedMC modules are activated and that only AdvancedMC modules with compatible software protocols are enabled.

In order that the MCH also recognises the plug-in CompactPCI modules, which have no management controller, and includes them in communications, the Advanced 'connection module' signals the entire CompactPCI zone as effectively one board to the MCH. Thus the CompactPCI zone is controlled via the Advanced 'connection module'.