GE PACSystems RX7i Cpu Programmer's Reference Manual

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GE PACSystems RX7i Cpu Programmer's Reference Manual Manual pdf 380 page image

GFK-2950C February 2018 365Chapter 8 Structured Text (ST) ProgrammingThe Structured Text (ST) programming language is an IEC 61131-3 textual programming language.This chapter describes how structured text is implemented in PACSystems. For information on usingthe structured text editor in the programming software, refer to the online help.The block types Block, Parameterized Block, and Function Block (UDFB) can be programmed in ST.The _MAIN program block can also be programmed in ST. For details on blocks, refer to ProgramOrganization in Chapter 2.8.1 Language Overview8.1.1 StatementsA structured text program consists of a series of statements, which are constructed fromexpressions and language keywords. A statement directs the PACSystems controller to perform aspecified action. Statements provide variable assignments, conditional evaluations, iteration, and theability to call built-in functions. PACSystems supports those statements described in StatementTypes.8.1.2 ExpressionsExpressions use operators to calculate values from variables and constants. An example of a simpleexpression is (x + 5).Composite expressions can be created by nesting simpler expressions, for example,(a + b) * (c + d) – 3.0 ** 4.