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Abstract
Several Automation Direct (DirectNet) Programmable
Logic Controllers (PLCs) have been integrated into the
accelerator control system at Jefferson Lab. The
integration is based on new software that consists of three
main parts: a PLC driver with a state machine control
block, a device support module, and a common serial
driver. The components of new software and experience
gained with the use of this software for beam dump
systems at Jefferson Lab are presented.
1 INTRODUCTION PLCs were developed in the late 1960’s to eliminate
the large cost involved in changing complicated relay
based machine control systems. These systems were
inflexible. Their major rewiring or complete replacement
was necessary every time when the production
requirements changed and control sequences had to be
modified. It became very expensive when changes were
frequent. The idea to replace relay systems with flexible