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 steppermotors. 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 the command protocol for each device is unique. This makes it difficult to design generic drivers for RS-232 and also hampers efforts to design generic troubleshooting methods. This paper presents software developed independently at three other labs and integrated into a single system 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 including 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.