74 TRUE TRUE Chapter Objectives After completing this chapter, you will be able to: •• Define and identify the functions of a PLC memory map •• Describe input and output image table files and types of data files •• Describe the PLC program scan sequence •• Understand how ladder diagram language, Boolean language, and function chart programming language are used to communicate information to the PLC •• Define and identify the function of internal relay instructions •• Identify the common operating modes found in PLCs •• Write and enter ladder logic programs Each input and output PLC module terminal is identified by a unique address. In PLCs, the internal symbol for any input is a contact. Similarly, in most cases, the internal PLC symbol for all outputs is a coil. This chapter shows how these contact/coil functions are used to program a PLC for circuit operation. This chapter covers only the basic set of instructions that perform functions similar to relay functions. You will also learn more about the program scan cycle and the scan time of a PLC. 5 Basics of PLC Programming Symbol Name XIC 0 FALSE FALSE 1 0 1 XIO Bit status Instruction status
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