FLAT CABLES

computers or digital equipment, and to interconnect units of the same computer together. We limit our discussion to I/O cables. The interfacing standards provide guidelines on the type and maximum cable length to be used for the I/O data cables. The number of conductors in each cable varies with type of computer. A cable can have from 2 to 120 conductors. The cable is grounded with a signal ground and/or to its common connector ground. If it has shielding, the shielding is also grounded to the connector (fig. 2-31). The cables must also be protected (shielded) from EMI and RFI. This is accomplished with a solid or braided covering of nonferrous conductive material, preferably copper. The cable is completely covered throughout its length. This insulated conductor or conductors provide high levels of RF attenuation to potential sources of compromising emanations (CE), such as RFI. This is not required for all cables; a shipboard environment and land-based operational sites, such as an ASWOC, are two examples of situations in which cables must be protected. We discuss some of the more common types of cables used for I/O transfer of data. They are flat, ribbon, twisted component, coaxial, and, fiber optic cables. FLAT CABLES. —Flat cables consist of multiconductors. They can have individually insulated round conductors (solid or stranded) or bare conductors sandwiched between layers of insulation. See figure 2-32 for an example. Flat cables can be terminated with single-piece pcb or card-edge connectors, two-piece plug and receptacle pcb connectors, rectangular multipin connectors, or IDCs. They can be used for parallel and serial transfer of data. They are used extensively with microcomputers. Figure 2-32.—Flat cable. RIBBON CABLES. —Ribbon cables are flat multiconductor cables with individual insulated conductors (usually solid) that can be easily separated. Figure 2-33 is an example of a ribbon cable. Ribbon cables are extremely flexible and can be bent around sharp turns. They can be terminated with single-piece pcb or card-edge connectors, two-piece plug and receptacle pcb connectors, rectangular multipin connectors, or IDCs. Ribbon cables can be used for parallel and serial data transfer. They are also used extensively with microcomputers. Figure 2-31.—Grounding a cable. 2-24 Figure 2-33.—Ribbon cable.