A client for Enron Modbus
Some of the work in this library could have been integrated into and already existing
python modbus library like riptideio/pymodbus.
Comparing the normal use cases for modbus, Encron Modbus doesn't differ that much but the
Operator Event, Alarm Event. Alarm Acknowledgement and History Readout
wouldn't really fit in another project
We are mostly interested in the History Readout feature and might not implement the
other special cases unless we need to.
from enron_modbus.client import EnronModbusClient
from enron_modbus.transports import SerialTransport
transport = SerialTransport(port="/dev/tty.usbserial", baudrate=9600)
client = EnronModbusClient(transport=transport)
client.connect()
print(client.read_numerics(1, 5160, 6))
print(client.read_numeric(1, 5160))
print(client.read_booleans(1, 1010, 2))
print(client.read_booleans(1, 1010, 33))
print(client.read_boolean(1, 1010))
client.write_boolean(1, 1010, True)
print(client.read_boolean(1, 1010))
client.write_numeric(1, 7001, 46)
print(client.read_numeric(1, 7001))
client.disconnect()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.
Each datatype has its own data table
| Data Type | Register Numbers | Data Address |
|---|---|---|
| Boolean | 1001-1999 | 0x03E9-0x07CF |
| 16-bit integer | 3001-3999 | 0x0BB9 to 0x0F9F |
| 32-bit integers | 5001-5999 | 0x1389 to 0x176F |
| 32-bit floats | 7001-7999 | 0x1B59 to 0x1F3F |
Difference from normal Modbus is that the register numbers are equal to the data address. Offset 0 instead of 1 as in normal Modbus.
| Code | Function |
|---|---|
| 0x01 | Read boolean (1xxx) |
| 0x05 | Set single boolean (1xxx) |
| 0x03 | Read numeric (3xxx, 5xxx, 7xxx) |
| 0x06 | Set single numeric (3xxx, 5xxx, 7xxx) |
There are two types of history tables, hourly and daily.
The achives are lists of historical item values with corresponding timestamp. The items included in the lists are defined in the modbus map. The tables sizes are also defined in the slave device.
The timestamp is for the end of the capture period (end of hour or end of day)
Each record is given a specific record number. This number rolls over 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.