No. 1 ESS ADF: Autonomous Data Scanner and Distributor

Equipment to perform the input/output function in a data-switching system handling a large number of connecting data lines has been one of the most expensive and space-consuming parts of the system. This is due primarily to complex handshaking requirements and to the need for handling addressing and all message text by the input/ output unit. To achieve an economical solution, a wired logic unit was designed with the extensive use of ultrasonic delay lines in a time-shared, multiplexed mode. This paper describes the system organization, the logic, and the circuits that are unique to the data-scanner distributor (DSD) for the No. 1 Electronic Switching System, Arranged with D a t a Features (No. 1 ESS A D F ) . Unique designs--such as the data line circuit, the delay-line memory loops, the addressing structure, and the control unit logic--are presented. Also, some of the unique maintenance features required for an autonomous wired logic unit that were employed are described. 2857 2858 THE BELL SYSTEM TECHNICAL JOURNAL, DECEMBER 1970