Unity Pro XL - read only variable issue

I have an ebool variable that I want to access via modbus as read only. This variable is set in the PLC logic when a tanks level is high. When I assign this high level bit an address of %I, Unity Pro does not compile saying that the bit is now read only. What is the usefulness of %I if you cant write to the bit! (aside from physical IO) If I make this a %M, dont I run the risk of this bit being changed from an HMI,driver glitch, etc? I have some bit that I DO NOT want modified by the outside world.

Thanks

What's a %I

%I is only for physical inputs.

If you want to use unchangable data in PLC you can put it into %KW memory area.

SCADA_Dude said:

If I make this a %M, dont I run the risk of this bit being changed from an HMI,driver glitch, etc?

Click to expand...

If your %M variable is calculated every scan cycle in the PLC there is no such risk.

Do %K even exist in Unity ?

If it is an input map your %I to an EBOOL then make that read only not the %I

To make it read only in the program right click it in the data editor got to properties and uncheck the RW program box.

You can also make it a constant in here too if you wish

%K does not exist.

As I understood, SCADA_Dude wants variable to be read-only only for external world, not for his program.

Why not do whatever calculation required in unmapped tags (so hmi can't reference them) and move the values into mapped variables to display the result. Then even if they are changed from outside it will have no effect (and the plc will just move the calculated value back over the changed values)