11. Connection to other devices11.4 Modbus TCP11.4.3 Modbus TCP error handlingRead Coils 0x01:In the event of an error, Modbus TCP will send an error frame.Fault Code 1 byte 0x81 ; Read CoilsException Code 1 byte 02 or 03 or 04Exception Code 02 = Invalid address, i.e.:l 0 (the user keeps specifying addresses as one-based addresses)l Undefined* (please refer to the "Modbus map" table) orl Un-enabled*Exception Code 03 = The number of outputs is not >= 0x0001 and <= 0x07D0Exception Code 04 = (Error in server) n.a.***For an error message, it is sufficient if only one of the requested addresses is notunlocked or is invalid.**Data in the image table is protected from other modules by semaphores; as of thiswriting, no known criterion for a "read coil" error in the server.Read Discrete Inputs 0x02:In the event of an error, Modbus TCP will send an error frame.Fault Code 1 byte 0x82 ; Read Discrete InputException Code 1 byte 02 or 03 or 04Exception Code 02 = Starting address is invalid, i.e.:l 0 (the user keeps specifying addresses as one-based addresses)l Undefined* (please refer to the "Modbus map" table) orl Un-enabled*Exception Code 03 = The number of inputs is not >= 0x0001 and <= 0x07D0Exception Code 04 = (Error in server) n.a.***For an error message, it is sufficient if only one of the requested addresses is notunlocked or is invalid.**A read operation always returns consistent data from the image table, since this datais protected from other modules by semaphores. In other words, as of this writing,there is no known criterion for a "read discrete inputs" error in the server.Read Holding Registers 0x03:In the event of an error, Modbus TCP will send an error frame.easyE4 11/18 MN050009 EN www.eaton.com 553
