ABSTRACT
Real-time systems have many common features as illustrated in Figure 1. This system controls the speed o f a servo-motor and performs some logical control. I t is also part o f a larger system and is linked to this system by a communications net work. There is provision for local communication wi th an operator. The speed measurement transducer provides an analog signal which has to be sampled and converted to a digital signal by an A D C (analog-to-digital-converter) and the mo tor controller requires an analog value which has to be converted from the internal digital representation by the D A C (digital-to-analog-converter). The logic control communicates via the digital input and digital output registers. Communication with the operator is via the input device and display device controllers and it is assumed that data is transferred between these devices in the form o f eight bit (byte) character codes. The data transferred to and from the communications con troller is in the form o f messages which are made up o f blocks o f A S C I I charac ters which are transferred character by character to the communications controller.
