Siemens Simatic M7-400 Reference Manual page 581

Bytes 9 to 24 of the SM 421; DI 16
Data record 1 with bytes 9 to 24 contains the channel-specific diagnostic data. The
figure below shows the assignment of the diagnostic byte for a channel of the
module.
Figure B-7
S7-400, M7-400 Programmable Controllers Module Specifications
A5E00069467-07
24/60 VUC
7 6 5 4 3 2 1 0
0 0 0 0 0 0
Configuring/parameter assignment error
Wire break
Diagnostic Byte for a Channel of the SM 421; DI 16 x 24/60 VUC
Diagnostic Data of the Signal Modules
B-7