The MicroTCA specification agreed in 2006 was initially orientated to the requirements of network edge and access areas in telecommunications networks. With suitable modifications, however, MicroTCA forms an ideal basis for high-performance systems in other market sectors. To adapt the system to the conditions of an industrial environment, for example, PICMG is currently developing the MicroTCA.1 sub-specification "RuggedMicroTCA for industrial air-cooled systems". The requirements for management and data transfer are also different in industrial applications from those of telecoms. Features such as redundancy, high availability, hot swap, e-keying etc are often not required. Meanwhile, more and more system solutions are being developed that are specifically tailored to the framework of industrial applications.

The MicroTCA specification (MicroTCA.0 R.1.0) extends the area of application of AdvancedMC modules. These modules were first defined for use as mezzanine boards in AdvancedTCA. For this there are special AdvancedMC carriers that are used in AdvancedTCA systems in place of AdvancedTCA blades. Now MicroTCA has taken these mezzanine boards and defined them as function modules that are inserted directly into the system.

AdvancedMC modules no longer adhere to the traditional euroboard format for plug-in boards of 3 and 6 U, but are now somewhat smaller with heights of about 75 and 150 mm respectively. Increasing miniaturisation of components and parts means however that it is possible today to realise complete single-board computers on these small boards. It is thus possible with MicroTCA to build extremely small systems with high processing power (Fig. 1). MicroTCA also uses serial data transfer via PCIe, Gigabit Ethernet, 10 Gigabit Ethernet, S-ATA or SAS and Rapid I/O and allows data transfer rates of up to 12.5 Gb/s per port. With four fatpipe ports available per module, a data transfer rate of 60 Gb/s is thus possible between two modules. A further advantage of MicroTCA is its integrated carrier and shelf management that allows e-keying and thus prevents damage through incorrect insertion and allows remote management of the system. This makes MicroTCA an interesting alternative for applications in those sectors where either remote management, high data rates or a very small construction is required.

Because MicroTCA was originally conceived for telecommunications, certain features must be adapted to suit the requirements of other market sectors. The minimum installation depth of a MicroTCA system is set at 197 mm, so that the system with front cabling will fit into the 300 mm deep ETSI racks that are commonly used in telecommunications. However, the installation depth of systems for industrial automation, instrumentation and control, medical systems, defence systems and traffic and transport systems are not restricted to such a short dimension. The climatic factors (temperature and shock and vibration parameters etc) are also different.

There is also a large difference in the system availability. The telecommunications market demands an availability of 99.999%. To achieve such a high availability, MicroTCA defines redundancy in all components such as ventilation, power supply, switches and all function modules. The specification even goes so far that the active carrier manager can decide, individually for each AdvancedMC module, which of the four possible power modules is to supply that module with power and which remain in standby mode, ready to take over the power supply without a time delay in case of failure.

In order to develop MicroTCA for markets other than telecoms, the standards and specifications of the respective markets must therefore be implemented. Those telecoms-specific features that are not required in the new application should also be trimmed away in order to optimise the system costs (Fig. 2).

The simplest modification is the redundancy. High system availability is rarely required in non-telecoms systems and so redundancy is not necessary. MicroTCA systems of this type are already available. These will use, for example, only one cooling unit, and thus the number of fans is halved. The number of power modules and AdvancedMC modules in the system is reduced likewise. Further, with no redundancy requirement, only one MCH (MicroTCA carrier hub) is needed, which reduces the size of and number of layers in the backplane and the number of connectors is halved.

The cooling unit is defined in MicroTCA as 'optional', which allows further potential for modification. In MicroTCA the fan speeds are normally controlled by the MCH; it is however equally possible to implement a simple fan monitoring system using a temperature sensor or even to dispense with fan control and monitoring altogether.

Where the user has only one system configuration, e-keying is also in certain circumstances not necessary. It is thus possible to omit the management element on the AdvancedMC modules. In any case the hardware costs of the MMCs (module management controllers) on the AdvancedMC modules are negligibly small.

There is, on the other hand, considerable savings potential in the area of the power supply. Rather than using a 600 W plug-in PSU in the smallest space, a conventional open-frame PSU can be used in conjunction with a power management board. Since the enclosure depth in industrial systems is not set to 200 mm, the PSU may be accommodated behind the backplane. There is thus also a gain of useable space in the board cage.

The MCHs are modularly designed to the MicroTCA specification. The carrier manager and basic communications are defined via GbE on the main board. The second MCH tongue defines the clock signals and storage interface, and the third and fourth tongue are defined for the fatpipe switch. This configuration in turn affords several possibilities for adapting the system to different requirements. PCIe is often used as the bus between the processor AdvancedMCs and I/O boards, and here one 2.5 Gb/s lane is often sufficient. It is then possible to assign these PCIe lanes from the processor AdvancedMC board directly to up to 8 slots and thus save use of the fatpipe switch on the MCH. The PCIe clock can be generated on an AdvancedMC module or on the backplane. Processor-to-processor communication is normally via Ethernet, and the 1GbE of tongue 1 of the MCH is normally sufficient for this.

The user can thus decide from the options described which functionalities are required and where costs can be saved. The management can easily be adapted to the most diverse of applications.

Particularly in transport and military applications, but also in industrial automation, a high level of shock and vibration resistance is often necessary. PICMG has therefore set up three MicroTCA sub-specifications to take care of these requirements:

1. MicroTCA.1: Air cooled ruggedized AdvancedMC modules and MicroTCA systems: solutions for air-cooled AMC.0 modules with higher mechanical and thermal requirements

2. MicroTCA.2: Conduction cooled ruggedized AMC modules and MicroTCA systems: solutions for 'contact-cooled' AMC modules with higher requirements, e.g. by bringing 'cold plates' into contact with hot spots.

3. Market-specific layered dot specifications: other requirements.

MicroTCA.1 is defined for industrial systems with air cooling and will be released shortly. This specification will make MicroTCA system solutions possible that meet the DL3 requirement class of IEC 61587-1. This includes peak accelerations of 25 g in shock tests and of 3 g in vibration tests, and represents a requirement higher than that for MicroTCA.0 by a factor of between almost 4 and 6. Such systems are used, for example, in situations with high vibration levels, e.g. on rotating machines (offset printing) and in railway and marine equipment.

The most important difference to the MicroTCA base specification is the clamping of the AdvancedMC modules onto the board cage. Only with this additional locking mechanism can the severe mechanical requirements of MicroTCA.1 be fulfilled. For the front panels of the AdvancedMC module this means that the locking mechanism must be extended in both vertical directions and fixed to the MicroTCA systems. It is particularly important that the locking is effected without any force being applied to the MicroTCA backplane connector. An 'ordinary' screw would, when turned, press the AdvancedMC subassembly board generally in the direction of the backplane and so apply a force onto the connector.

Here Schroff has developed a functioning and both mechanically and electrically tested AdvancedMC module fixing that fully satisfies the requirements of the MicroTCA.1 specification and allows locking without pressure on the connector. This solution (Fig. 3), for which Schroff has registered a patent, is a component of the MicroTCA.1 specification. A bushing (blue) fixed to the front panel serves to accept an expansion plug (green) with an inner funnel. The screw(grey) has a geometry that corresponds to that of the funnel of the plug. When screwed in, the plug expands and becomes jammed positively against the bushing fixed to the front panel. No resultant force (pressure) occurs in the direction of the backplane connector. This solution - as being the only one to date - is visually documented and given a Schroff order number in the appendix to the specification.

There is already a large spectrum of processor-AdvancedMC modules on the market, and many telecoms-specific modules. At present however there is a lack of I/O boards for industrial applications. Here again, however, a solution has already been found. A MicroTCA single-module board cage can be integrated into an ordinary 3 U 19" board cage. With this MicroTCA hybrid system (Fig. 4) users have the possibility of working with two technologies in parallel. A special AdvancedMC module that sends PCIe via cables to a special CompactPCI board, can thus connect the parallel CompactPCI bus to MicroTCA. Then all existing CompactPCI and PMC I/O boards can also be used in a MicroTCA environment.