Linak TECHLINE LA35, Руководство по установке, Страница: 19 / 44

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Exceptions
When a MODBUS master transmits a request to a slave the expected behaviour is that the slave responds with a
normal response. But several error scenarios are possible:
• The slave does not receive the request due to a communication error. No response is returned;
the master will process a time-out and eventually repeat the request.
• The slave receives the request but detects a parity or CRC communication error. No response is
returned; the master will process a time-out and eventually repeat the request.
• The slave receives the request without a communication error but cannot handle it. The slave
will in that case return an exception response informing the master about the nature of the error.
Exception response message:
Exception codes are:
Addr Function Error CRC
Slave
Address
Function
Code
+80
hex
Error Code
Exception
Code
Definition Description
01 Invalid Function The message received is not an allowable action
02 Illegal Data Adress The register address(es) referenced in the function-dependent data
section of the message is not valid
03 Illegal Data Value The data value of the referenced address is not within limits
04 Slave Device
Failure The addressed device is not able to process a valid message due to a
bad device state