Finding the base address in SIMATIC Manager

In the SIMATIC manager, follow these steps

1. Open the project
2. Expand the tree and then click on the name of the PLC.
3. Double click on hardware.

You should have this view

The base address is located in the table in the bottom of the window. In our case, the column I address contains the DI-base-address and the column Q address contains the DO-base-address. The same would apply for analog I/O modules.

Finding the base address in TIA portal

In TIA portal, follow these steps

1. Open your project
2. Switch to project view
3. Expand the tree of the project
4. Expand the subtree of the CPU
5. Double click on device configuration

In this case, the DO-base-address is 8. There is no other base address on this PLC.

Controller base address

SIEMENS controllers use a separate process image for input and output, and therefore the input and output addresses overlap. However, the analog modules have sequential addressing (contiguous process image for Analog IOs). With SIEMENS, you also have the ability to modify the module address by hand.

SIEMENS	Analog	Digital
Input	0 + offset 1 + offset .. .. n + offset	0 + offset 1 + offset .. .. n + offset
Output	0 + offset .. m + offset	0 + offset .. m + offset

The offset mentioned above is handled internally by the library. The user, unless there is a special case, should not care about.

For more information, check the SIEMENS peripheral addressing documentation.