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5
Chapter
Slave Response
■ Normal Slave Response
The slave creates and replies with a response message for each command message. The response message has the same
format as the command message.
The contents of the data part are different depending on the function code.
■ Irregular Slave Response
If there are problems (such as specification of a nonexistent function code) with the contents of the command message other than
transmission error, the slave creates and replies with an error response message without following the command.
The composition of the error response message uses the value of the function code in the command message plus 80
H, as seen
below.
The error code is shown as follows.
■ No Response
In the following situations, the slave will ignore the command message and not send a response message.
• The station number specified by the command message is not the same as the slave’s specified station number.
• The error check code does not correspond, or a transmission error (such as parity error) is detected.
• The interval between the data comprising the message is empty for more than 24 bit time.
• The slave station number is set to "0".
Refer to
See "Chapter 6, Message Details".
Field name No. of bytes
Station No. 1 byte
Function Code
+80
H
1 byte
Error Code 1 byte
Error Check Code (CRC-16) 2 bytes
Error Code Contents Explanation
01
H
Faulty function code A nonexistent function code was specified. Please check the function code.
02
H
Faulty address for coil or resistor The specified relative address for the coil number or resistor number cannot be
used by the specified function code.
03
H
Faulty coil or resistor number The specified number is too large and specifies a range that does not contain
coil numbers or resistor numbers.
Refer to
See Section 5 "Transmission Control Steps" (p. 25).
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