Appendix C. ENIP-2: IEC 60870-5-101 and IEC 60870-5-104
ENIP-2, manual, ENIP.411187.002. Rev. 11.2020
78
Link transmission procedure
Address field of the link
Balanced transmission
Unbalanced transmission
Not present (balanced transmission
only)
One octet
Two octets
Structured
Unstructured
Frame length
255
Maximum length L (control direction)
255
Maximum length L (monitor direction)
5 - repetitions Time during which repetitions are
permitted (Trp) or number of repetitions
When using an unbalanced link layer, the following ASDU types are returned in class 2
messages (low priority) with the indicated causes of transmission:
The standard assignment of ASDUs to class 2 messages is used as follows:
Type identification
Cause of transmission
A special assignment of ASDUs to class 2 messages is used as follows:
Type identification
Cause of transmission
1, 3, 11, 13, 15, 30, 31, 35, 36,37
<3>
NOTE: In response to a class 2 poll, a controlled station may respond with class 1 data
when there is no class 2 data available.
IEC 60870-5-104
Frame format FT 1.2, single character 1 and the fixed time out interval are used exclu-
sively in this companion standard.
Link transmission procedure
Address field of the link
◼
Balanced transmission
◼
Unbalanced transmission
◼
Not present (balanced transmission
only)
◼
One octet
◼
Two octets
◼
Structured
◼
Unstructured
Frame length
◼
Maximum length L
When using an unbalanced link layer, the following ASDU types are returned in class 2
messages (low priority) with the indicated causes of transmission:
◼
The standard assignment of ASDUs to class 2 messages is used as follows:
Type identification
Cause of transmission
◼
A special assignment of ASDUs to class 2 messages is used as follows:
Type identification
Cause of transmission
