PCI for Industrial Computers

CompactPCI is based on the electrical functionality of desktop PCI and the Eurocard physical form factor. It is designed for ruggedized applications in industrial environments. CompactPCI boards have several features that make them ideal for embedded systems or for industrial PCs:

• High density 2mm pin and socket connectors
• Designed for vertical card racks for better cooling
• Excellent vibration and shock protection characteristics
• Shield for EMI/RFI protection
• I/O connections on front or rear of module
• Staged power pins for hot swapping

Form Factor

The key to the CompactPCI bus is a gas-tight, high-density pin and socket connector that meets the IEC-1076 international standard (pictured below). Its low inductance and controlled impedance make it ideal for PCI signaling. The connector uses a 2mm "Hard Metric" connector and has 47 rows of 5 pins per row, with a total of 220 pins (15 pins are used for the keying area). An additional external metal shield is also used. The large number of ground pins ensures adequate shielding and grounding for low ground bounce and reliable operation in noisy environments. By controlling impedance, the connector can minimize signal reflections.

CompactPCI 220 pin connector

CompactPCI boards must follow one of two size specifications and have ejector handles that are IEEE 1101.10 compliant. 3U boards measure 100mm x 160mm, and 6U boards measure 233.53mm x 160mm. The 3U boards have a single ejector handle and use a 220 pin connector for all power, ground, and all 32- and 64-bit PCI signals. This connector consists of two halves - the lower half (110 pins) is called J1 and the upper half (also 110 pins) is called J2. Twenty pins are reserved for future use. 3U boards that only perform 32-bit transfers can use a single 110 pin connector (J1). For example, Quatech's QSCP-100 serial CompactPCI serial board is a 32-bit 3U board using a single J1 connector. Both 32-bit and 64-bit 3U boards can be mixed on a single CompactPCI backplane.

Quatech QSCP-100, 3U CompactPCI board

6U boards can have up to three additional connectors (J3-J5) with a total of 315 2mm style pins, and because of their large size use two ejector handles. The CompactPCI specification only defines signal-pin assignments for J1 and J2. J-3 through 5 can be user defined based on application requirements. They can also be used as a bridge to other buses like VME or ISA in hybrid backplanes. PICMG is developing future specifications for a standardized use of the additional connectors.

CompactPCI form factors for 3U and 6U boards

CompactPCI Systems

The CompactPCI system is made up of CompactPCI bus segments, each of which has one system slot and up to seven slots for CompactPCI peripherals (at 33MHz). The system slot is used to control the peripherals attached to the bus segment. For example, it provides bus arbitration, clocking, and reset functions, as well as system initialization functions. It can be located at any position in the backplane, and must use both J1 and J2 to control both 32-bit and 64-bit peripheral boards. The peripherals in the remaining seven slots can be simple boards, intelligent slaves or PCI bus masters. By using PCI-PCI bridge chips, the CompactPCI bus can be expanded in 8 slot increments.

Peripherals attached to the first four CompactPCI connectors are provided a unique CompactPCI interrupt. After that, rotating interrupts are assigned to allow boards to share interrupts. The System Slot board always has its own interrupt. Rules for interrupt sharing are derived from the specification governing PCI bridges. Note that because some devices require more than one interrupt, interrupt sharing may be required even if only the first four slots are used.

CompactPCI is designed to use both +5V, and +3.3V devices. +V(I/O) power pins are designed for universal boards that can operate at either +5V or +3.3V. A keying technology is used to prevent a board from being attached to the wrong power pins. Universal boards are not keyed. Backplanes have both +5V and +3.3V, and, depending on the application, Universal boards can use either. Typically, for 5V operation a brilliant blue coding plug is used on the backplane, for 3.3 V operation a Cadmium yellow coding plug is used. Power terminals can be located on the front, rear or side of the backplane.

CompactPCI for Data Communication

CompactPCI boards are designed for ruggedized, industrial environments. They are also ideal for many embedded systems that are implemented in such environments. Though they are electrically similar to standard PCI boards, CompactPCI boards cannot be used in a desktop computer without a special adapter board. They are made to be used in specialized enclosures designed to provide both superior protection against environmental hazards and easy access for rewiring, replacing, or exchanging peripherals. To that end, the pin sequence on the backplane connector is staged to support hot swapping.

Quatech serial PCI boards with the "IND" option are also designed for use in industrial environments. However, to implement protection on the board itself requires sacrificing speed. The CompactPCI specification is specifically designed for such environments, and can optimally implement data communication peripherals in them.

cPCI Specs
Bus Clock Signal		33 MHz
Bus Width		64-bit
Theoretical Max. Transfer Rate		132 Mbytes/sec (1 Gbit/sec)
Advantages		designed for industrial use, hot swapping/Plug & Play, ideal for embedded systems
Disadvantages		lower speed than PCI, need adapter for PC use, incompatible with older systems

Click here to see how cPCI compares with other busses.