Analysis and implementation of the IEC 61131-3 software model under POSIX Real-Time operating systems

In this paper, we present a proposal to implement the IEC 61131-3 software model. This model establishes the high-level elements of the Programmable Logic Controllers. We discuss some of the points of the standard that should be clarified before implementing it, such as concurrency, variable scope and cyclic operation. We show the implementation guidelines using POSIX compliant Real-Time Operating Systems, in particular RTLinux running on PCs. A translator has been implemented accepting textual descriptions following the IEC 61131-3 standard.