Siemens SIMATIC S7-400 Installation Manual page 59

Channel on an Analog Module
Channels on analog modules are addressed word-wise.
Starting with the default address of the module, which also represents the address
of the uppermost channel of the module, the addresses of the individual channels
(from top to bottom) increase by two bytes (= one word).
This is clarified by the following figure with the example of a digital input module
with 8 channels at slot 6 (default address 832). With an analog input module, the
first characters are IW instead of QW.
Automation System S7-400 Hardware and Installation
A5E00850741-01
Channel addresses
QW 832
QW 834
QW 836
QW 838
QW 840
QW 842
QW 844
QW 846
Addressing the S7-400
3-7