Understanding Sysmac Studio Variable table

[Man_G]

Hi

I would like to know and understand  what does  AT stand for in the  AT column of variable table in Sysmac  Studio.  As a newbie in the OMRON PLC environment, I would like to have a clear understanding and knowledge of this software. 

[Parky]

In Sysmac Studio, the AT variable attribute is used to explicitly assign a variable to a specific physical memory address or to link an internal variable to a system-defined variable (like an axis or I/O variable). 

Direct Memory Access: For older communication protocols like FINS or specific hardware interfaces that require physical memory addressing, the AT keyword allows you to map a symbolic variable (For example My_Var) to a physical memory location (e.g., %Mxx). This makes it compatible to many things like an HMI that can only communicate using physical addresses.

The New IEC 61131 tries to get away from physical addressing in favour of symbolic in other words rather than have the fixed like I 0.0 Q 1.3 M200 & D23 you just use a symbolic name

However, Sysmac & others actually assign physical addresses to the existing fixed memory areas when compiled but HMI's & the like do not know where the location is so that is the reason, In RSL5000, they have ditched the physical fixed addressing & the compiler & runtime system uses purely symbolic addressing. there must be a physical allocation table somewhere that knows the allocated physical address, Mitsubishi do the same as Omron so still use physical addresses at compile time.

[Man_G]

Ta, for such a simple and brilliant explanation MrPLC🫡!!

[Crossbow]

For most cases, you never touch the AT column.  If you are making variables for inputs and outputs, they are assigned on the I/O Map screen.  You can see what connection is assigned by reading the text of the AT column, it will show the connection point for the data.  This applies to the local and networked devices.

You can however still force old fashioned Omron PLC addresses, and that is really only used for backward compatibility with an HMI or data collection product that cannot import the variables.  As an example, if you want to store an integer value to D0, you would create a variable and then set the AT column to %D0.  This is absolutely a backward compatibility thing, and is not required in order to properly use the PLC.  In fact, I believe in some of the newer PLCs, you actually need to go into parameters and enable those memory addresses if you intend to use the old style.