Peripheral System

Other articles in this issue describe the overall system organization and the processor complex with its busing and pulse distributing facilities. 1, 2 This article describes the major functional peripheral blocks of the system: the scanners, the network, the peripheral decoders and the trunks and service circuits. Electronic scanners may be broadly defined as circuits which sense or detect the absence or presence of voltage or current. In No. 2 ESS, scanners are used to detect the on-hook, off-hook status of a customer's line, to check the status of talking paths for flash and disconnect, to monitor certain test points in various frames and to scan other miscellaneous points about which information is desired. In a certain sense, the scanners may be thought of as the primary source of information to the control complex regarding the actual physical state of the customers and circuits associated with the outside world. 2669 2670 THE BELL SYSTEM TECHNICAL JOURNAL, OCTOBER 1969 2.1 Ferrods The ferrod is the sensing element used in No. 2 ESS.3 A single ferrod consists of a ferrite rod or stick, approximately the size of a large paper match, around which is wound a pair of solenoidal control coils. Threaded through two holes in the center of the ferrite stick are hairpin single-turn interrogate and single-turn readout windings. Figure 1 is a diagram of a ferrod. To determine the state of the ferrod, a 0.5 amp bipolar pulse is applied to the interrogate winding. The positive half cycle, approximately 3 microseconds long, switches the ferrite around the holes, as TO CUSTOMER L I N E , JUNCTOR, TRUNK, OR OTHER CIRCUIT TO BE SENSED OR SUPERVISED