MOV , LIM syntax question

Hi all,

I am going through a code at my company's PLC and i came across these two instructions (see attachment).

I am familiar with have addresses specified in 'source' but this declaration seems a lot confusing. Anyone explain what these syntax are?

Thanks!

In the "LIM" instruction if the value in tag "RO.Sys_Program_Loaded" is within the limits of
12 to 13 (constants) or equal to 12 or 13 the instruction is true.

In the "MOV" instruction a value of one ( constant) is moved to tag "RO.Sys_Step_Number" if rung condition preceding the MOV instruction are true.

The LIM instruction is an input checking to see if a certain condition exists. It is basically saying:

Is RO.Sys_Program_Loaded Greater than or Equal to the Low Limit of 12

AND

Is RO.Sys_Program_Loaded Less than or Equal to the High Limit of 13

If the value being tested is within that range, the instruction is true. Else, it is false

The MOV instruction on the other hand is an output that writes to the Destination.

So, when the logic ahead of the MOV is true, the constant number of 1 will be written to RO.Sys_Step_Number.

In the graphic you provided, the current value of 38 would be overwritten with the value 1. Sort of like a reset.

** EDIT ***
As usual, Mickey was faster!


OG

Thanks Mickey & OG!

Also, in the LIM, is 14 the stored in RO.Sys_Program_Loaded? Does that mean the the LIM block will always output false (as it does not fall under the limits).

Yes, 14 is the present value of RO.System_Program_Loaded, and this LIM will be false unless and until RO.System_Program_Loaded falls to somewhere between 12 and 13.

The built-in help files for those two commands in RSLogix 5000 are very descriptive and give great examples.

14 the stored in RO.Sys_Program_Loaded?

Click to expand...

But how a value of 14 got there we would have to see the whole program.

OZEE said:

The built-in help files for those two commands in RSLogix 5000 are very descriptive and give great examples.

Click to expand...

If you find negotiating the help system tedious, try this....

On any instruction, click on the instruction itself (the name if it is a box instruction like LIM), and hit F1 on your keyboard. You will be taken directly to the help for that instruction without having to select it in the help system.

One more hint about finding instructions in the help system: If you know the name of the instruction click the alphabetical listing option on the top line in instruction help to show instructions grouped alphabetically instead of by category.