An IPC with motherboard is a standard PC with a 19” enclosure. This is comparable to a Sport Utility Vehicle (SUV). A SUV is not able to pull a plough even though it is an off-road vehicle.

The problem of direct plug-in inside as described above is not solved in the case of an IPC with motherboard. The mounting of standard PC plug-in cards is solved within the scope of the limited possibilities of non-standardized PC card dimensions. In addition, the critical component “power supply” is not sufficiently considered.

In case of service the IPC has to be dismounted and opened before getting through to the plug-in card. Compared to CompactPCI, the advantages are lower costs, due to the use of mass-market components.

The customer has the choice: Is a standard PC enough for the application, is a 19” enclosure necessary, or do you require higher reliability and serviceability which only a CompactPCI system can fulfill?

Although PCI has gained most of its recognition as a local bus for 80x86 based PCs, PCI is at the core of all modern microprocessor designs. PowerPC and DEC's Alpha, for example, are supported with chip sets with PCI interfaces and can be easily implemented on CompactPCI. In fact, CompactPCI is the industrial bus that does the most justice to these very high performance new chips, giving them a system bus with all the bandwidth that these chips are capable of.

Yes. Each CompactPCI bus is limited to eight slots for electrical loading reasons. This can be easily expanded with PCI-PCI bridge chips, available from a number of manufacturers. The bridge chip acts as a sort of "super buffer" chip. Interrupts, plug-and-play information, and data are easily and generally automatically transferred across the bridge. A bridge chip usually exacts a one clock penalty ( generally about 30 nanoseconds) per transaction. If the data transaction is a burst mode type - transferring hundreds or thousands of bytes at a time - this overhead is extremely small. One advantage of bridge chips is that each side of the bridge can be performing data transfers to cards on its side of the bridge simultaneously.

One of the advantages of CompactPCI is the high contact density of its connectors J1 and J2. They provide far more signals on the backplane than actually necessary for the PCI bus. Serial interfaces, Ethernet channels, USB terminals, fan control or warning devices are examples for CPU modules that can be available via J2. Digital and analog outputs of I/O modules are possible as well.

These signals are routed through the backplane to a Rear Transition or Rear I/O board. The Rear I/O board looks like a shortened Eurocard and also has a front panel with additional connectors.

Thus, it is possible to feed all cables into the back. The CPU and peripheral components can easily be accessed from the front. Another important aspect is the protection of cables. The Rear I/O cabling for example is inside the switch cabinet where it is protected against mechanical wear and tear.

The third aspect seems far fetched but is far from unimportant: In case of service the module does not need to be touched preventing COM1 and COM2 from being mixed-up and avoiding other errors. Searching for an error which had its source in two mixed-up channels is certainly a common experience.

The staged (multi-length) pins in the CompactPCI connector cause some connections to be made before others when inserting a card. The reverse occurs when a card is removed. This, in principle, allows CompactPCI products to be hot swapped. This is a complex issue, however, and significant efforts are underway by a number of PICMG member companies to develop a quality solution. There are some significant obstacles to be overcome. First, special circuitry must be developed so that a board can be inserted and removed from a live, operating PCI bus. Second, DC power to boards being hot swapped must generally be ramped up and down to avoid "glitching" the system's DC bus. Thirdly, applications software and operating systems must be developed that recognize when a board is removed and another inserted. This will be required to re-initialize complex I/O chips like graphics adaptors or network interfaces. Despite these obstacles, however, hot swap is a very desirable feature and a great deal of energy is being devoted to developing viable techniques.

The modules height and width as well as all their accessories are standardized in a 19-inch frame for use in industrial applications worldwide. The resulting advantages for larger systems or complex installations are clear. On the outside, a subrack of normal width measures 482.6 mm (= 19”). However, absolute dimensions are rare in daily use.

The internal spacing is divided in Horizontal Pitch (HP). A 19” subrack has 84 HP. Due to the height of the electronic components (on the module), 4HP is defined as the minimum width. Up to 21 modules therefore fit into an 84 HP subrack. If modules consist of more than one board, e.g. CPUs, the module grows in steps of 4 HP. The same applies to I/O modules requiring more space for front panel connectors. In this case a module may need 8 or 12 HP.

The subrack’s height is specified by Units (U) in the 19” system. Subracks for simple Eurocards usually have 3 U (dual Eurocards have 6 U). Further accessories like a fan unit with 1 U or space for cable conduits or similar can also require any other design.

If subracks do not require the entire width, systems with 3 U / 32 HP or 4 U / 24 HP or any other combination are possible. However, the spacing of 1 HP / U is maintained to avoid proprietary designs.

Height x depth: Eurocard 100 x 160 mm, dual Eurocard 233.35 x 160 mm.

First of all, the disadvantages of 3 U systems: Due to a smaller board the layout is more difficult and requires more consideration and effort in order to place the desired functions. In addition, the halved front panel never provides enough space for external connections. Why do we still try?

From a mechanical point of view the 3U size is more resistant, better fixed in the subrack and therefore less susceptible to shocks and vibrations. This alone would be an argument to justify the higher developmental effort.

With 3U boards the module’s type and number can be more easily adapted to the application.

Beyond this there is another effect: The available mounting space is rather short in height than in width. Of course this statement has to be considered empirically. Please reflect on your last three projects: Did you have any space problems? If yes, in height or width or in both dimensions?

Yes, you can. The technically advanced state of the CompactPCI system should leave no room for surprises. Though having said that, difficulties might arise in case of driver and software support for (third party) modules. Problems in this area can sometimes lead to changing the third party supplier.

A PCI module like it is found in a normal PC (with PICMG 1.x standard) needs to be both mechanically and electrically integrated in a 19” subrack. This is possible only with great efforts, requires space, and should only be done in case of emergency. However, the problem of direct plug-in is not solved. Such an adapter is available in the open market.

In addition, an ISA module needs to be converted from the ISA bus to the PCI bus (ISA/ PCI bridging). This can only be realized for certain functions and needs to be considered from case to case.