User`s manual

6-10
6.5 MODBUS Communication Protocol
INP-TN5A0202-E
Slave response
Normal slave response
A slave creates and replies the response message to each command message. The slave response message uses the same
format as the command message. Contents inside the data part vary according to function codes.
Irregular slave response
If there are problems (such as specifi cation of a nonexistent function code) with the contents of command messages other
than transmission error, a slave creates and sends back an error response message without running the command.
The composition of an error response message is as follows. The function code uses the value that the function code of the
command message plus 80H.
Field Name Number of Bytes
Station No. 1 byte
Function Code + 80H 1 byte
Error Code 1 byte
Error Check Code (CRC-16) 2 bytes
The error codes are shown below.
Error Code Contents Explanation
01H Function code failure
A nonexistent function code was specifi ed. Check the
function code.
02H Address failure for coil/register
The specifi ed relative address for the coil No. /the register
No. cannot be used by the specifi ed function code.
03H Coil/register/limit failure
The specifi ed number of words is too many and specifi es
the range that does not contain the coil No./register No.
The specifi ed data is specifi ed beyond the limit.
06H Busy state
Data is been writing in the register. Retrying
communication after more than 100- sec interval.
No slave response
In the following cases, a slave ignores the command message, and send the response message back neither.
In the case that the station number specifi ed by the command message is not the same as the station number specifi ed for
a slave.
In the case that the error check code does not correspond or the transmission error (such as parity error) is detected.
In the case that the interval between the message composing data is 24 bit time or more.
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