Siemens SIMATIC Manual page 587

Byte 7 channel fault vector and up (data record 1)
Figure B-4
The channel fault vector is at least 1 byte long. For modules with more than 8 channels, the
channel fault vector occupies several bytes.
The channel-specific diagnostics data comes after the channel fault vector; refer to section
Channel-specific diagnostics data (Page 588).
If another channel type is available (see Figure "Bytes 4 to 6 of diagnostics data"), the
channel type with the same structure as that described above (channel type, length of
diagnostics data, number of channels of the same type, channel fault vector, channel-
specific diagnostics data of the channel type) follows after the channel-specific diagnostics
data.
S7-300 Module data
Manual, 06/2017, A5E00105505-AJ
B.2 Structure and content of diagnostics data, byte 0 and up
Byte 7 of diagnostics data
Diagnostics data of signal modules
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