DVP- ES2/ EX2/ SS2/ SA2/ SX2/ SE&TP O pe r a t i on Ma nua l - Pr ogr am m i ng5- 25.1 Step Ladder Instruction [STL], [RET]Mnemonic Operands Function Program steps ControllersES2/EX2 SS2 SA2 SX2STL S0~S1023 Starts STL program 1Explanation:STL Sn constructs a step point. When STL instruction appears in the program, the main program willenter a step ladder status controlled by steps. The initial STL program has to start from S0 ~ S9 asinitial step points. The No. of Step points cannot be repeated.Mnemonic Operands Function Program steps ControllersES2/EX2 SS2 SA2 SX2RET None Ends STL program 1Explanation:RET instruction indicates the end of a step ladder program starting from S0 ~ S9, i.e. the executionreturns to main program after RET is executed. Maximum 10 initial steps (S0 ~ S9) can be appliedand every initial step requires a RET instruction as an end of STL program. With the step ladderprogram composed of STL/RET instructions, SFC can perform a step by step control process.Program Example:Step ladder diagram:M1002ZRST S0 S127SET S0SET S20Y0SET S30Y1SET S40Y2S0RETENDX0S0SS20SX1S30SX2S40SX3SFC:S0S20S30S40S0M1002X0X1X2X3Y0Y1Y25.2 Sequential Function Chart (SFC)In the application of automation control, a seamless combination between electrical control andmechanical control is required for completing an automation process. The sequential control ofautomation process can be divided into several steps (states). Each step is designated with own
