Improvement of VME control system for vacuum devices and magnet power supplies of the PLS storage ring

In the Pohang Light Source storage ring, there are 12 VME systems, called VMMIU, in the local control sheds around the storage ring. The VMMIU's control and monitor vacuum devices, gate valves, LCW, injection system, and magnet power supplies. All vacuum devices and magnet power supplies have local controllers. These controllers are connected to the VME system through RS422/RS232 serial communication. Now we are upgrading software and hardware of these VME systems to enhance device execution speed and communication reliability. In this paper, we describe control structure and scheme of both the current VME system and the upgraded one.