5.3 Modbus RTU
5-39
Chap. 5 USING STANDARD RS-485
5.3.2.5 Error response
If an incorrect query is received, the query is not processed and an error response is returned.
Error response
1 byte 1 byte 1 byte 2 bytes
Station No. Exception function Sub code Error check
Interpreting "Error response"
This is the same as for a station number request. The exception function adds 128 to the FC of the
query message.
For example, if FC = 3, then exception function = 3 + 128 = 131 (83
H
). The subcode indicates the
reason for the exception, as shown in the table below.
Sub code Item Details
M26
(HEX.)
Keypad
1 Incorrect FC FC other than 3, 6, 8, 16 received 75
(4BH)
01
Incorrect function
code
Range exceeded or non-existent code (F81, etc.)
received
Incorrect data size Attempted to write more than 16W of data
2 Incorrect address
Diagnosis code error
(maintenance code)
Diagnosis code setting is not "0"
78
(4EH)
02
3 Incorrect data Data range error Write data range exceeds writable range 80
(50H)
03
Link priority Attempted to write command data or run
command data with field option (T link, SX,
etc.) applied
76
(4CH)
7 NAK
Write disabled (1) Change during operation disabled
(2) Write disabled (Read only, M range)
(3) Link function edit allowed mode
(4) Write via RS-485 disabled
(H31, H34-37, H40, P02)
(5) F04, F05, P03-P27
(M1 motor parameters protected)
79
(4FH)
07
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