Autonics krn100 series, User Manual

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2 Modbus TCP protocol
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2.7 Exception process (Exception Response-Error Code)
If communication error occurs, it sends response command and transmits the applicable
Exception Code after setting(1) the highest-level bit of received commend (Function).
MBAP Header
Function
(Command)
+80 H
Exception Code
7Byte 1Byte 1Byte

ILLEGAL FUNCTION(Exception Code: 01 H): Command is not supported.

ILLEGAL DATA ADDRESS(Exception Code: 02 H): Starting address of the queried data is
inconsistent with transmittable data address.

ILLRGAL DATA VALUE(Exception Code: 03 H): The number of the queried data is
inconsistent with the number of transmittable data.

SLAVE DEVICE FAILURE(Exception Code: 04 H): Not properly completes the queried
command.
The below example is to read the output status (ON: 1, OFF: 0) of non-existing coil 001001(03E8
H) on the Slave from the Master.

Query (Master)
MBAP Header
Function
(Command)
Starting Address No. of Points(Number of data)
High Low High Low
00 0d 00 00 00 06 01H 01 H 03 H E8 H 00 H 01 H

Response (Slave)
MBAP Header
Function (Command)
+80 H
Exception Code
00 0d 00 00 00 03 01H 81 H 02 H