Which addresses do the inputs/outputs of the S7-200 expansion modules receive?
Inputs and outputs are always addressed in an 8-bit grid from x.0 to x.7, even if there are not in actual fact so many real connections available.
Digital inputs and outputs of a CPU have fixed addresses that always begin with I0.0 or Q0.0. Depending on the number of real connections available the addresses are assigned in order (e.g. I0.0 to I0.7 and I1.0 to I1.7 etc.).
The sample CPU in Fig. 1 has 14 inputs, i.e. inputs I0.0 to I0.7 and I1.0 to I1.5 are available. Inputs I1.6 and I1.7 are not there physically, but are still addressed to complete the pattern. However, these "placeholders" cannot be used by the program nor can they be assigned to any successive expansion module.
Digital inputs of expansion modules are handled in the same way. However, compared with the CPU they have no fixed addresses, but are added to the (real and virtual) inputs available on the left of the module.
If an expansion module is integrated between two existing modules, all the addresses to the right of the new module change. Fig. 3 shows this sort of change of configuration.
Analog inputs and outputs are always assigned in pairs and are always addressed with even numbers (AIW0, AIW2 and AQW0, AQW2 etc.). If there is only one real connection on a module, the second is addressed but not used.
Detailed information on this topic is available in the paragraph entitled "Accessing the Data of the S7-200" in the chapter entitled "PLC Concepts" of the S7-200 System Manual, order number 6ES7298-8FA24-8AH0 (Entry ID: 1109582).
S7-200, Expansion modules, Input, Output, Address