System Interfacing for On-line Computer Control

Abstract

On-line computer control of Numerically Controlled (NC) machine tools and associated peripheral equipment such as the large electrograph plotter is considered with a view to the problems of interfacing. The system interface connects the Benson-Lehner plotter to the minicomputer in a behind-the-tape-reader (BTR) mode. A simulation of the actual signals from the bus-bar of the minicomputer is built so that it will be a relatively simple job to make the final connection. Also the transmission link between the computer and the plotting system requires high reliability of data transmission. The signals at the BTR unit and computer interface are of serial form but in order to link the units over a distance it is necessary to interpose some form of transmission system. The transmission lines have been built using twisted pairs with an overall screen to minimise inductive and capacitive coupling. The transmitter unit accepts characters in a parallel form and transmits them in serial form with the appended control and error detecting bits. The system is capable of transmitting digital data at various rates dependent upon the demands of the peripheral unit under control.