Siemens SIMATIC S7-300 Manual page 397

Structure of double data word in Standard Mode
Double data word structure of the encoder inputs:
Structure of double data word in Fast Mode
Double data word structure of the encoder inputs:
In the double data word from channel 0, the status of digital input IO is reported to bit 27
(digital input status) and the double data word from channel 1 is reported to digital input I1. In
the double data word from channel 2, the bit is always = 0.
Output address in Standard Mode
No output data are supported in Fast Mode.
S7-300 Automation System Module data
Manual, 08/2006, A5E00105505-04
7.4 Position decoder module SM 338; POS-INPUT; (6ES7338-4BC01-0AB0)
Other signal modules
7-17