how can i stop download mistake

how can i stop down load wrong prog. to wrong PLC
(EX.machine 1prog to machine 2PLC)
we use ethernet comunication

dont select the wrong program!

This is a housekeeping aspect to me, if you have multiple machines with different programs they should be named/numbered accordingly..ie machine 1 = serial # 4567 plc name is 4567-1 machine 2 - serial # 5678 plc name is 5678-2

This is just an example but when its all said and done you will need to know WHAT machine you are connected too and if the program you are using is the correct version.

I dont know of a way for the PLC to say "HEY STUPID I AM MACHINE ONE, THATS MACHINE TWO'S PROGRAM.

Could it be, perhaps, that you are using TCP/IP addressing?

Those addresses must be unique!

Be sure that each station is uniquely assigned in software at the particular station.

If the station addresses at each station are identified by DIP Switch, ensure that those addresses are unique.

Please come back and indicate your result.

What brand and model of controllers are you using out there in LA ?

Some PLCs have a CPU serial number that can be accessed by the application program. It wouldn't keep the wrong program from being loaded, but it would keep it from trying to run the machine.

Some communication software also features "Paths" and "Shortcuts" that help you organize your programs and keep them pointed at the correct controllers.

An Example

Just to follow up on what Ken and Terry have suggested, here is a code fragment that I include in most of my AB PLC-5 projects:

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The dip switch settings for the DH+ address are available to the PLC ladder (in the lower bits of S:2), and I make sure that, even though there may not be a DH+ network in the plant, the DH+ address is unique for the PLC.

The code compares the expected value of the dip switches to a number that is coded in the program. If there isn't a match, the TND instruction makes sure that the rest of the program can't be executed.