Enron Modbus Read Alarm Event

Read Event/Alarm Register

Request

To request events, function code 3 is used to request register # 32 (hex 0020).
This command is requesting events from the slave with address 1.

01 03 0020 0001 85C0

01: The Slave ID
03: The Function Code
0020: The Data Address of the event log. (20 hex = 32)
0001: Number or events requested (ignored - response will include the max # )
85C0 : The CRC (cyclic redundancy check) for error checking.

Response

This is a typical alarm event response to the event request shown above.

01: The SlaveID
03: The Function Code
14: Data bytes to follow (14 hex = 20)
8000: Alarm change bit map [ 1000 0000 0000 0000]
1B5F : The register that triggered the alarm change (7007)
483366C0 : Time Stamp 32 bit float HHMMSS (183707.0 = 6:37:07pm)
47EAF800 : Date Stamp 32 bit float MMDDYY (120304.0 = Dec 3,2004)
40200000 : Current (alarmed) value of variable 32-bit float (2.5)
00000000 : Unused at this time (zero filled)
C2C8 : The CRC (cyclic redundancy check) for error checking.

The alarm change bit map is:
      
bit 0   0   unassigned
bit 1   0   unassigned
bit 2   0   unassigned
bit 3   0   unassigned
bit 4   0   unassigned
bit 5   0   unassigned
bit 6   0   unassigned
bit 7   0   unassigned
      
bit 8   0   unassigned
bit 9   0   Operator change event identified bit ( 0 = Alarm change)
bit 10 0   LoLo limit
bit 11 0   Lo limit
bit 12 0   Hi limit
bit 13 0   HiHi limit
bit 14 0   Rate of change limit
bit 15 1   Set/reset Alarm ( 1 = set, 0 = reset)