Enron Modbus

Reading Event/Alarm Register

Operator Event

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: The Slave Address
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 operator event response to the event request shown above.

01 03 14 0201 1B5F 483366C0 47EAF800 40800000 40200000 2D08

01: The Slave Address
03: The Function Code
14: Data bytes to follow (14 hex = 20 decomal)
0201: Operator change bit map [0000 0010 0000 0001]
1B5F: The register that changed (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)
40800000: Previous value of variable 32-bit float (4.0)
40200000: Current (new) value of variable 32-bit float (2.5)
2D08: The CRC (cyclic redundancy check) for error checking.

The operator change bit map is:
      
bit 0   1   Fixed value
bit 1   0   Zero Scale
bit 2   0   Full Scale
bit 3   0   Operator entry work value
bit 4   0   Boolean fixed bit
bit 5   0   Fixed/variable flag
bit 6   0   Table entry change
bit 7   0   System command change
      
bit 8   0   unassigned
bit 9   1   Operator change event identified bit
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 0   unassigned

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