Abstract: An inexpensive cable is utilized to permit multiple identical shelves in a bay of interface units to be wired for a plurality of signals by utilizing conventional twenty-five pin wiring. Hand-wired dedicated cables normally used for routing alarm signals are avoided. Printed wiring backplanes are utilized for connecting the common signals together and for permitting appropriate connections for the plurality of individual signals to be connected to the appropriate interface units positioned in the bay. The backplanes have an identical pattern so that the interface units can be used interchangeably.

Abstract: A printed wiring board including a first solder mask covering a portion of a first conductor pad. The inner perimeter of the first solder mask extends radially inward of the outer perimeter of the first conductor pad so that a portion of the first connector pad proximate its outer perimeter is covered by the first solder mask. The inner perimeter of the first solder mask is radially outward of the inner perimeter of the first connector pad so that a portion of the first connector pad proximate the inner perimeter of the first connector pad is left exposed. In addition, the printed wiring board may include a second solder mask that covers a portion of a second connector pad. The second solder mask configured with respect to the second connector pad similar to that of the first solder mask with respect to the first connector pad. Alternatively, or in addition to the second connector pad, the printed wiring board may include a conductor path of which at least a portion is covered by a second solder mask.