In S-7 siemens PLC how to go for I/O addressing. Is I/O addressing require symbol table or variable table. Whats difference between local data & global data.

 

The first step in working with Siemens PLCs is hardware configuration. In hardware configuration you can do I/O addressing.

Install Step7 V5.3, in documentation of Simatic you have a PDF file named "STEP 7 - Configuring Hardware with STEP 7", I think you should read this first.

 

You can address the I/Os only in symbol table. You can use variable table only to monitor the status of inputs, outputs and memory flags as well, which you used in your program.

But you should go through the Hardware configuration and programming manuals that are available as PDF files before entering in and programming.

 

When configuring your hardware(I/O modules etc.) in Hardware Configuration, the software automatically addresses the I/O for you depending on the slot. For example, if you define 32 bits DI module in slot 4, the system would address byte 0 to 3 for this slot.
The first bit would have address I0.0 and the last bit is I3.7.

Symbol table is for you to define symbol. Symbols are names you defined for each I/O. You could also define symbols when configuring your hardware.

Global data are I/O address and Memory. You could define these data in any program block.

Local data are data that you defined in program block such as OB, FC and FB. The local data are used within the block. If you open OB1, you could see that there are pre-defined local data at the top section of the block. And, you could add some for your programming needs.
Local data are defined as IN, OUT and TEMP etc.

 

Dear Xavier,

Thank you so much for the details. I just wanted to confirm whether it's possible, say, after hardware configuration programming has been done. I opened that program & I wanted to know which I/O are used where (instead of looking in blocks for which FB or which FC has been used for that particular I/O). Is it possible to generate or enlist I/O list which has been used in the program? Kindly guide me.

 

Dear Sandy,

There's a way to see used I/Os in the software.
Open Simatic Manager, open your CPU, then open your blocks.

Now do the following:
Options >>> reference data >>> display
or press CTRL + ALT + R directly.

Now, you'll have 5 options of view. You can choose cross reference (you can see used I/Os, memory area, timers, DBs... etc. with their symbolic names and their locations in the software.)

Another choice is to make assignment, and you will see I/Os in the form of bytes, and the used I/Os will be marked by X. Use a filter to alter between inputs, outputs, timers and other types of data.

I hope you find this useful.