CHAPTER 13 RS-485 COMMUNICATIONS
Modbus RTU Communications 13-27
13
(2) Exceptional code field
Exceptional responses from slaves are returned as exceptional response which indicates exceptional
content with the query.
Exceptional
code
Description and sample queries
01h
Incorrect FC (An incorrect FC is specified.)
・An FC other than 01h, 03h, 05h, 08h, 0Fh, and 10h, which are supported, is specified.
02h
Incorrect address (An incorrect address is specified)
When FC 03h or 10h is specified
・An address not listed in [Table 13-1] data addresses list is specified.
・The address that is listed only for FC 03h in [Table 13-1] is specified for FC 10h.
When FC 01h, 05h or 0Fh is specified
・An address not listed in [Table 13-4] coil data addresses list is specified.
・The address that is listed only for FC 01h in [Table 13-4] is specified for FC 05h or 0Fh.
When FC 17h is specified
· The write data specified address is other than 6000h to 6007h,
and the read data specified address is other than 6000h to 600Fh.
When corresponding address in 6000s is specified with FC 03h or 10h
· The read data address specified with FC 03h is other than 6000h to 600Fh.
· The write data address specified with FC 10h is other than 6000h to 6007h.
03h
Incorrect data (An abnormal value is specified in the information field.)
When FC 03h or 10h is specified
・The following value is specified as the no. of registers: zero, odd number, or a value
exceeding the maximum value.
・A value different from the no. of registers is specified to the no. of data bytes.
・A value out of range is specified to a write data.
When FC 01h, 05h or 0Fh is specified
・The following value is specified as the no. of coil data: zero, or a value exceeding the
maximum value.
・A value different from the no. of coil data is specified to the no. of data bytes.
・A value not specified as ON/OFF values is specified to a coil data in FC 05h.
When address in 6000s is specified with FC 17h
· The number of registers is 0 or an odd number, or a value that exceeds the maximum
value is specified.
· The value specified for the number of data bytes is in disagreement with the number of
registers.
· A value outside the following ranges is specified for read and write data.
･ The number of read data items exceeds 16.
･ The number of write data items exceeds 8.
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