Embedded controllers, field bus and a modular I/O concept: central elements of BESSY II controls

Wherever applicable I/O nodes connected by a field bus (FB) have apparent advantages: Simple and flexible installation and cabling, easy signal conditioning as well as data filtering and process security provided by intelligent actuators and sensors. The cost of a complex 3rd control system layer may be a high development effort. At BESSY several design principles of this layer control the risk: A few multi purpose I/O cards form a modular set. Multiple I/O bus connectivity provides high installation flexibility. 'Controller Area Network' (CAN) is the FB connected to the VME system of the standard model control system. Communication is provided by a small set of software modules designed to be easily adapted to hardware changes. The communication protocol with BESSY I/O modules is a small and efficient subset of the 'CAN Application Layer' (CAL) standard.