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- Byte mode - allows working with devices that implement the registers as 1-byte variables (in contrast with Modbus standard in which the register value is 2 bytes).
- Variable mode - allows working with devices that implement the registers with different sizes than standard 2 bytes. It was implemented because of support of the flowmeter FloBoss 103 made by Fisher Controls International (at this time a part of Emerson Process Management): 1-byte variables, 4-byte unsigned/signed integers, text strings of length 10,12,20,40 characters, a 6-byte time stamp, and other.
Note: this mode enables work with devices implementing the so-called Enron Modbus or Daniel Modbus. - Passive (scanning) mode allows to work in eavesdropping mode. This applies especially to serial communication when the communication port of the device is already used to communicate with another Master device. Due to the nature of the Modbus protocol, it is necessary to receive both requests and responses in this mode.
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The attached ZIP contains the configuration of two lines and two stations with the MODBUS Client/MODBUS Server protocol that communicate via TCP (MODBUS Server listens on a TCP port 9999). Data written through one line is received through the other line. Four I/O tags are configured on each line (Float, with address 3.0, Signed with addresses 4.0 and 4.1, and Bool with address 1.0). MODBUS Server I/O tags values are controlled by the system second (Sec) and use linear conversion (Float is divided by 1000, Signed with address 4.0 is multiplied by 10). The value of the Bool I/O tag is controlled by the eval tag P.TrueFalse, which changes the value True/False every second.
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The attached ZIP contains the configuration of the line, station, and I/O tags for communication with an Emerson chromatograph that implements MODBUS DANIEL®.
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You can read blogs about the Modbus protocol |
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