An uncommon cause for the -01 result is a device with an incomplete implementation of
Modbus. Some devices do not fully implement parsing Modbus commands. Instead, they are
hardcoded to respond to certain Modbus messages. The result is that the device will report an
error when you try selectively polling registers. Try requesting all of the registers together.
Result code -02: illegal data address
The illegal data address error occurs if the slave rejects the combination of starting register and
length used. One possibility, is a mistake in your program on the starting register number. Refer
to the earlier section about register number and consult the device documentation for support
information. Also, too long of a length can trigger this error. The ModbusMaster() instruction
uses length as the number of values to poll. With 32-bit data types, it requests twice as many
registers as the length.
An uncommon cause for the -02 result is a device with an incomplete implementation of
Modbus. Some devices do not fully implement parsing Modbus commands. Instead, they are
hard coded to respond to certain Modbus messages. The result is that the device will report an
error when you try selectively polling registers. Try requesting all of the registers together.
Result code -11: COM port error
Result code -11 occurs when the datalogger is unable to open the COM port specified. For serial
connections, this error may indicate an invalid COM port number. For Modbus TCP, it indicates a
failed socket connection.
If you have a failed socket connection for Modbus TCP, check your TCPOpen() instruction. The
socket returned from TCPOpen() should be a number less than 99. Provided the datalogger
has a working network connection, further troubleshooting can be done with a computer
running Modbus software. Connect the computer to the same network and attempt to open a
Modbus TCP connection to the problem slave device. Once you resolve the connection between
the computer and the slave device, the connection from the datalogger should work.
7.3 Internet communications
See the Communications specifications (p. 173) for a list of the internet protocols supported by
the datalogger.
7. Communications Protocols 91
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