What is Enron Modbus?
Enron Modbus is a modification to the standard Modicon modbus communication protocol. It was developed by Enron Corporation. The main differences between the two protocols is the numbering of the register addresses, the support of 32 bit registers as well as 16 bit, and the ability to transmit Event logs and Historical data.
How is data stored in Enron Modbus?
In Enron Modbus, there is a different table for each of the different data types.
Information is stored in the Slave device in four different tables.
Each value in a table has a data address and a
corresponding register number.
Unlike Standard Modbus, in Enron Modbus the Register Numbers are equal to the Data Addresses. For example, Register Number 7001 has Data Address 1B59 (7001 in hexadecimal). The offset is 0 for all Enron Modbus Registers.
What function codes are used in Enron Modbus?
A Function code is sent by the master to select a table and command type (read or write).
What are the formats of Enron Modbus commands and responses?
Follow the links in this table to see examples of the requests and
How are events transmitted?
There are two kinds of events, Operator events and Alarm events.
The Slave device will store at least 100 of the most current events, including both operator and alarm events.. A numeric variable called the Event Index is typically mapped to a 7000 series numerical variable so it can be read. The Event Index is the number of events that have occurred since the event buffer was last read.
The response from the slave will contain all the events that have occurred since the last collection. If more than 255 events have occurred, only the earliest 255 will be transmitted. If no events have occurred, the slave sends a response containing no data values.
After an event transmission, the master can send an acknowledgement message to the slave to reset the Event Index and clear the event log.
What is the format of an event request and response?
There is only one command for both types of events. The type of event is shown in the response.
This link shows an example of the request with an Enron operator event response.
This link shows an example of the request with an Enron alarm event response.
This link shows an example of the Enron
request and response.
How is history transmitted?
The Daily and Hourly Archives are lists of historical item values with specific time stamps.
Each record is given a specific record number. This number wraps back to zero when the table fills up and the device starts writing over old data. The most current record numbers are recoded in variables called the Hourly Index and Daily Index. These index variables are typically included in the map as 7000 series numerical variables so they can be read.
What is the format of a historical record request?
This link shows an example of the Enron history request and response.
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