PLC Programming (Ladder Logic) - Siemens Simatic Industrial Software -The seven steps of the Ladder Logic program "Micro Win 32 Step 7 V 3.1" are shown in the following figure. The ladder 1-2-3-4 can be used to multiply two numbers by entering 1-2 at node A, Node B, and so on to get the answer at node X. Node X outputs 1 for entry 01 and 49 for entry 49. The cycle ends at Node D with an output of 56 for an input 1+5=6. Z = 56. Ladder Logic also has a number of commands that makes programming easier, such as *JOB, *CLR, *RST, *ON. The command *JOB repeats the subroutine it precedes. The subroutine is not repeated if the subroutine is not defined with an asterisk (*). The command *CLR resets all outputs to off or low. The command *ON turns on all outputs equal to an asterisk (*); e.g., 03* turns on all outputs 03. The Ladder Logic program "Micro Win 32 Step 7 V 3. 1" is shown below. The asterisk (*) symbols are used throughout this example to highlight commands. Step 1- "Load Inputs" The program starts at the beginning of the program. The line for step 1- "Load Inputs" reads: *PLUS*00001,00100,00310,00400,00020,20320 The program must start with a *PLUS symbol because it is used in other parts of the program to indicate that a value is being added to an input variable. A value is added if the asterisk symbol - indicates that an input variable can be multiplied by another input variable. Step 2- "Carry Out Commands" The line for step 2- "Carry Out Commands" reads: *NOT(07)*00010,00100,00301,00030,20320 The subroutine for step 2- "Carry Out Commands" adds 1 to the input variable 07 by using the *NOT command. The *NOT command subtracts the input variable 7 from the input variable 0. The result of this calculation is output to node B with an asterisk (*) symbol. Step 3- "Complete Commands" The line for step 3- "Complete Commands" reads: *CLR*00010,00020,00030,00301,00100,20320 A *CLR command resets all outputs to off or low. This command is being used in this program to set the input variable 09 back to 0. The asterisk (*) symbol in front of the input variable 09 is necessary because a *CLR command resets all outputs back to 0. The *CLR command also resets the output variables 00100 and 00200 to their original configurations before being changed by previous calculations. 8eeb4e9f32 54
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