1 Modbus RTU Protocol
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1.8 Exception response-error code
If occurs an error, send a response command and transmit each Exception Code after set(1) the
highest-level bit of received command (Function).
Slave address
Function
Exception
1Byte 1Byte 1Byte 1Byte 1Byte
ILLEGAL FUNCTION (Exception Code: 01 H): A command that is not supported
ILLEGAL DATA ADDRESS (Exception Code: 02 H)
: Starting address of queried data is inconsistent with transmittable address from the
device.
ILLEGAL DATA VALUE (Exception Code: 03 H)
: Numbers of queried data are inconsistent with the numbers of transmittable
(transferable) data from the device.
SLAVE DEVICE FAILURE (Exception Code: 04 H)
: Not properly completed the queried command (order).
Read the output status of non-existing coil 001001 (03E8 H) [ON: 1, OFF: 0] on Slave (Address
17) from Master.
Query (Master)
Slave address
Function
11 H 01 H 03 H E8 H 00 H 01 H ## H ## H
Response (Slave)
Slave address
Function
+80 H
Exception Code
11 H 81 H 02 H ## H ## H