With the rapid growth of open-bus-architecture computers in the late '70s, there was a need to standardize the hardware for multivendor compatibility. Many of these computers were being installed into the popular 19-in. racks. The International Electrotechnical Commission (IEC) subcommittee 48D created a document which standardized the hardware based on the two-piece DIN (41612) connector also known as the IEC 603-2 connector.
In 1984, the IEC 48D committee approved the IEC 297-3 Dimensions of Mechanical Structures of the 482.6-mm (19-in.) Series—Part 3: Subracks and Associated Plug-in Units document. This standard covers the basic dimensions of a modular range of subracks for mounting in equipment according to IEC 297-1 (19-in. racks); and the connector-dependent dimensions used when two-part connector types, according to IEC 603-2 (two-part DIN 41612), are mounted on the subracks and plug-in units. It also specifies the standard positions of connectors such that plug-in units are mechanically interchangeable in subracks.
In 1987, the IEEE 1101 working group approved a standard that defined the dimensions and tolerances required to ensure mechanical function compatibility. This standard also offered integration guidelines with the intent of reducing design/development times and manufacturing costs. This mechanical format was known as the "Eurocard form factor."
VMEbus: The Eurocard form factor became a popular mechanical standard offering multivendor availability, reduced costs, and interchangeability. VMEbus, the most popular industrial bus structure since the mid '80s, was one of the first open-bus architectures to utilize this mechanical format. Other buses like Multibus II, VXI, Nubus, as well as other proprietary bus designs, adopted the Eurocard form factor. Due to the development of many additional mechanical standards that were based on the IEEE 1101 standard, a new numbering system was created. IEEE 1101 became a family of standards distinguished by IEEE 1101.X. The original IEEE 1101 document became IEEE 1101.1, and was approved in 1991.
In the mid '90s, with the widespread use of the VMEbus, designers were looking for more features to enhance it. The result was a committee under the VITA Standards Organization called the VME64x (VME64 Extensions) working group. VITA 1.1 would be the document that defined the added features to VME64 (VITA 1-VME64 was a previous enhancement to VMEbus, adopted by the VSO in 1995).
Many of these new features impacted the mechanical standard, prompting the formation of another IEEE committee to incorporate these new features. This committee was known as the IEEE 1101.10 working group. This working group, in conjunction with the VME64x working group, extended the mechanical features of IEEE 1101.1. Some of the features include EMC shielding, an insertion/extractor handle, ESD protection, an alignment pin, protective side covers, and mounting details for an expanded IEC 603-2 connector.
CompactPCI: In the early '90s, a local-bus standard was created to provide a high-speed interconnect for peripheral devices. The PCI standard became the predominant local-bus standard in desktop PCs. A group of manufacturers decided to leverage the circuitry and low-cost components and software availability, and package this into the Eurocard form factor using a 2-mm hard-metric connector. This design became know as CompactPCI. The IEEE 1101.10 standard was approved by the working group in July 1996.
EMC Shielding: With the CE requirements in Europe, many system integrators are looking for ways to improve the EMI/RFI shielding of the subrack. One major area of concern is the subrack's front aperture. Many of the existing designs require that the subrack be embedded into an enclosure to provide sufficient protection from EMI/RFI. Users are requesting easy access to plug-in boards for upgrades, repairs, or modifications. The IEEE 1101.10 standard, in conjunction with the IEEE 1101.1 standard, defines the mechanical and the interface dimensions for multivendor front panels to interoperate in a subrack. A gasket is provided on each front panel, which makes contact to an adjacent front panel. The front panels of the plug-in modules can now be exposed for user accessibility.
Injector/Extractor Handles: With the increased pin count in the expanded DIN/IEC connector and the additional J0 connector in VME64x, there came the need for a handle that would provide the leverage to overcome the insertion/extraction forces of the connector(s). Forces can be as high as 175 lbs. in the VME64x-P boards defined by the physics community. As mentioned, the CompactPCI bus selected the 2-mm connector. These insertion forces can be as high as 120 lbs in a fully configured 6U slot. The IEEE 1101.10 standard defines an injector/extractor handle and interfaces in the subrack to help in this area.
Keying: The IEEE 1101.10 standard defines provisions for keying for those applications that require slot exclusivity. When a plug-in board and slot are properly keyed, the plug-in card will fit into that slot. If the keys do not match, the plug-in board can't be inserted into the slot far enough for the two-piece DIN/IEC connectors to fully engage.
This feature is useful in applications where the user-defined pins of the bus structure may cause the system to be inoperable—or worse, cause damage to the plug-in board and/or backplane. The keying system defined in the standard will allow up to 4096 programming possibilities per slot.
Alignment Pin: The IEEE 1101.10 standard defines an alignment pin with the following features: assurance of parallel connector mating, an option for a front-panel ESD contact, and alignment for the shielded front panel. The alignment pin is located on the front panel assembly, and interfaces with the alignment pin receptacle in the card guide.
ESD Protection: The IEEE 1101.10 specifies two important features that help provide ESD (electrostatic discharge) protection:
- Card Guide ESD clip: A plug-in board may acquire static buildup while outside of the system. When the plug-in board is inserted into the system, the charge might discharge though the backplane connector, disrupting or even damaging the system. A feature in the card guide discharges any built up static from the plug-in board into the card-guide ESD clip, which is connected to the subrack frame ground. Depending on the design, the plug-in board may make continuous contact to the subrack frame, or may break contact to the frame prior to connector engagement.
- Alignment Pin ESD clip: Plug-in board front panels may conduct static through the system integrator or technician handling them. The IEEE 1101.10 standard defines an alignment pin that can provide a discharge path to the subrack frame.
Protective Side Covers: The standard defines a protective side cover for those applications requiring solder side protection to plug-in boards. These covers provide mechanical protection to the ESD gasket of an adjacent board as well as the solder tails or surface-mount devices on the solder side of the board. This cover also provides electrical protection from adjacent boards when the plug-in board is inserted or extracted from a live system.
Card Guides: The IEEE 1101.10 standard defines the dimensions of the card guide to allow intermateability with the plug-in boards. Other defined features are the keying chambers, alignment pin chamber, and provision for ESD contacts that can be built into the guide.
Card Guide Mounting Rails: The standard defines the feature in the mounting rail for injector/extractor surfaces. These surfaces allow the handle to inject or extract the plug-in board. The standard also defines the dimensions to allow multivendor handles to work with any IEEE 1101.10-compatible subrack.