Siemens S7-400 installation manual Geographical and Logical Addresses, Geographical Addresses

Addressing the S7-400

3.1Geographical and Logical Addresses

Addresses

In order to control a process, you must address the channels (inputs and outputs) of the signal modules from the user program. You must establish a unique assignment between the (geographical) location of a channel and an address in the user program.

Geographical Addresses

The geographical address of a particular channel is permanently assigned. It is governed by the physical location of the input or output. In particular, this depends on the following basic conditions:

•In which rack (0 to 21) is the signal module fitted?

•At which slot (1 to 18 or 1 to 9) in this rack is the signal module inserted?

•Which channel (0 to 31) of this signal module is addressed?

Section 3.2 describes the method of establishing the geographical address of a channel.

Logical Addresses

The logical address of a module and, therefore, of a channel is freely selectable. It is used in the program to address (read or write to) a particular input or output. The physical location of the relevant module need not be known during programming.

You establish the assignment between logical and geographical address with STEP 7.

The Two Stages of Addressing

You assign the channel address in two stages:

•Determine the geographical address of the channel from its location in the entire configuration.

•Assign a logical address to the geographical address under STEP 7. This logical address is used for addressing the channel in the user program.

Note

If your S7-400 comprises only a CR without ER, you can also use default addressing.

3-2	Automation System S7-400	Hardware and Installation
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