History Mechanism
General Description
The Modbus history registers enable the user to track the occurrence of specific events and their corresponding dates.
4 event histories are available:
-
Alarm history: the alarm history format corresponds to a series of 10 records. Each record is composed of 5 registers describing one alarm. See Alarm History.
-
Trip history: the trip history format corresponds to a series of 17 records. Each record is composed of 7 registers describing one trip. See Trip History.
-
Maintenance operation history: the maintenance operation history format corresponds to a series of 10 records. Each record is composed of 5 registers describing one maintenance operation. See Maintenance Operation History.
-
BSCM module event history: the BSCM module event history format corresponds to a series of 10 records. Each record is composed of 5 registers describing one BSCM module event. See Event History.
History Mechanism
Each event is time-stamped using the ULP DATE format.
When the history is full, the oldest event record is discarded to make room for the most recent event record, which is pushed to the top of the history.
The records are ordered in decreasing occurrence time, the most recent occurrence is in the first record.
The following tables describe the history mechanism for a 10-record history format:
Before event E
Record |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
10 |
Event |
E-1 (most recent event) |
E-2 |
E-3 |
E-4 |
E-5 |
E-6 |
E-7 |
E-8 |
E-9 |
E-10 (oldest event) |
After event E
Record |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
10 |
Event |
E (most recent event) |
E-1 |
E-2 |
E-3 |
E-4 |
E-5 |
E-6 |
E-7 |
E-8 |
E-9 (oldest event) |
After event E, event E-10 is lost.
History Reading
A read request is necessary to read a history record (see Modbus function read n input words, function code = 4, in Read Functions). For example, a read request of 5 registers is necessary to read the most recent alarm record of the alarm history format (see Alarm History).
Furthermore, to read the last n records of a history format, a read request of (m) x (n) registers is necessary, where m is the number of registers that compose the record.
For example, a read request of 7 x 3 = 21 registers is necessary to read the most recent 3 trip records of the trip history format (see Trip History):
-
The first 7 registers describe the first record of the trip history format (most recent trip).
-
The next 7 registers describe the second record of the trip history format.
-
The last 7 registers describe the third record of the trip history format.
When not used, history registers return 32768 (0x8000).