ladder logic program examples lamp sequence

Just like a LBL, only it is for use with the JSR. The processor immediately moves to the corresponding SuBRoutine. JSR.The Jump to SubRoutine is equivalent to the BASIC gosub statement. LBL is like a line number or marker in your program that can be used by the JMP instruction. Any logic that is skipped is not executed at all as long as the rung containing the JMP is true. The processor immediately JuMPs to the LaBeL in the JMP instruction. JMP.A jump is the equivalent of the BASIC goto statement. This is true for A/B processors, but I can't say with certainty it's true for all PLCs.

Any references to that coil (address) that are used later in the program will contain a 1. This happens even before the next branch is evaluated. So, if the output instruction is a coil (OTE), it is 'turned on' (at least in the output image table) right then. When the processor evaluates a rung or branch to be true, it immediately executes the output instruction(s) at the end of the rung or branch. Input instructions are evaluated to either true of false.

Instructions.There are input instructions and output instructions. This looks like a mistake on the part of whoever created this document: I think it should show that contact as true. Looking again at the example cited in your first post, It appears that Scan 1 shows a false contact in the first rung on the second branch. I have got myself confused here with the step 1 where the processor does the same thing I guess (or ladder scan is completely different from the way PLC works).Īs my question is on how a ladder scan works I really want to know when a particular coil is turned on by the instructions before it, does the contact associated with the coil which is present in the following rung turns on too in the same scan of the ladder or is it reflected in the next scan as is explained in the examples given by Phil in his section in Learn PLC.Īlso afer reading the post by Ron I have become interested in knowing how would a Jump instruction get executed? is it similar to what we see in normal programming languages or is it different.Īny replies would help me in going further. In the step 2 where it is mentioned that processore puts a 0 or a 1 in the bit depending on the command it sees while scanning the ladder. Going throught Ron's post has helped me to divide the scan and try to understand it but has also raised several questions in my mind.įirst of them is what exactly is meant by an instruction(I believe they are the different contacts and function that we write in the ladder diagram which governs the behaviour of output from PLC).

Ladder logic program examples lamp sequence