Use the EXTRN instruction to identify the external symbol that represents data in an external source module, if you want to refer to this data symbolically.

For example, you can identify the address of a data area as an external symbol and load the A-type address constant specifying this symbol into a base register. Then, you use this base register when establishing the addressability of a dummy section that describes this external data. You can now refer symbolically to the data that the external area contains.

You must also identify, in the source module that contains the data area, the address of the data as an entry symbol.