An I/O subnet for the APS control system-the BITBUS universal gateway

The Advanced Photon Source (APS) control system is based on a distributed topology of microprocessor-based Input/Output Controllers (IOCs). Since the cost effectiveness of placing an IOC near every point where an interface to the control system is required may be prohibitive, I/O subnets implemented via message passing network protocols are utilized. For greatest flexibility, such a subnet must support connections to equipment via discrete I/O points, connections to standard interfaces such as GPIB and RS232, and be a practical network for custom-designed interfaces to intelligent equipment. This paper describes the BITBUS Universal Gateway (BUG), a device which supports the different interfaces mentioned above with a connection to a single BITBUS distributed subnet. The BUG utilizes an interchangeable set of circuit boards, which allow for a commonality among interface points, and the ability to use commercially available modules for I/O. This approach also circumvents several limitations of GPIB and RS232, which restrict their use in industrial, electrically harsh environments, via an implementation of the BITBUS protocol over optical fibers