Page 93 - Programmable Logic Controllers, Fifth Edition - Mobile version
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Basics of PLC Programming
Symbol Name Bit status Instruction status
0 FALSE
XIC
1 TRUE
0 TRUE
XIO
1 FALSE
Chapter Objectives
Each input and output PLC module terminal is After completing this chapter, you will be able to:
identified by a unique address. In PLCs, the in- • Define and identify the functions of a PLC memory
ternal symbol for any input is a contact. Similarly, map
in most cases, the internal PLC symbol for all • Describe input and output image table files and types of
outputs is a coil. This chapter shows how these data files
contact/coil functions are used to program a • Describe the PLC program scan sequence
PLC for circuit operation. This chapter covers • Understand how ladder diagram language, Boolean
only the basic set of instructions that perform language, and function chart programming language are
functions similar to relay functions. You will also used to communicate information to the PLC
learn more about the program scan cycle and • Define and identify the function of internal relay
the scan time of a PLC. instructions
• Identify the common operating modes found in PLCs
• Write and enter ladder logic programs
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