Information-Control Software for Handling Serial Devices in an EPICS Environment

Each accelerator control system has a variety of measurement devices. One of the most common types of instrument interfaces used for their control is a serial (RS-232) bus. It is inexpensive and adequate for relatively simple measurement and control devices such as switchers, amplifiers, voltmeters, and stepper motors. Since the RS-232 specification is very broad and does not require uniformity above the basic communication protocol level, one of the major problems associated with the use of RS-232 is that a fundamental understanding of the details of each device's command protocol is required. This makes writing reliable control software difficult and also hampers efforts to design effective, generic troubleshooting methods for RS-232. This paper presents software developed at Jefferson Lab to handle serial devices in a generic manner. The software is based on the EPICS toolkit and uses a 3-tier architecture which includes a common serial driver at the bottom, a top-level protocol to specify individual device commands in a generic manner, and a mid-level of software to glue the two together