GE Fanuc 9030 External Read/Write

I am converting our Boiler project to a RX3i. Looking at some of the registers for the HMI I see 100r. It is labeled B_1_GPM (Boiler 1 Gallons Per Minute). The question is 100r is a word and has many initial Values. I noticed in the Variables tab there are 35 other B_1_GPM[00] ..."..."[01] and so on to 35. When I click on any one of these it has a working value it is displaying and it says external READ/WRITE. This is pulling data form power meters through Modbus. it has a Ethernet card which we use to program and pull data from. How can these registers be displaying values and getting an external read and write. Thanks.

The variable "B_1_GPM" is an integer array of 36 elements assigned to addresses %R100 - %R135. B_1_GM[00] is %R100. B_1_GPM[01] is %R101... B_1_GPM[35] is %R135.

The BLK_CLR instruction at rung number 1 clears all 36 elements at power-up.

Assuming that the PLC is the ModbusTCP master, somewhere in your logic there should be logic setting up COMMREQ instructions that fetch the data from the power meters. The external Read/write designation is necessary to make the variables accessible to the HMI.

Steve thanks These registers are not set up with the Modbus COMM_REQ I see now in the program that a Analog AI is moving the values into these registers. But what was or is confusing to me is the External READ/ WRITE is greyed out and you cannot change it back to False or Internal. Is it because once you define the variable as External READ/WRITE it cannot be changed? This had a Alphanumeric Display coprocessor years ago maybe it has something to do with why it is greyed out?

You can't change it while you're online with the PLC. Go offline and you can change it. When you go back online you'll be "Not Equal" so you'll have to download.

Steve it is greyed out while offline. I can change the 100R but not any of the [00] or rest of the 35. Is this normal for this type of variable.

You can't change individual elements of an array. You have to change the entire array. Select the top level variable. The one that's visible when the array is not expanded in the variables list.

Thank you Makes perfect sense now..All I wanted to do was change the name of the variable.. If I change the variables it might be easier for the next one to figure it out. Thanks Again...