Autonics TF3 Series, User Manual

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1 Modbus RTU Protocol
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1.8 Exception Response-Error Code
When communication error occurs, send response command and transmit exception code after
setting (1) the highest level bit of received command (Function).
Slave Address
(address)
Function
(C8
0 H
Exception Code
Error Check(CRC16)
Low High
1Byte 1Byte 1Byte 1Byte 1Byte

ILLEGAL FUNCTION(Exception Code: 01 H): Not supported command

ILLEGAL DATA ADDRESS(Exception Code: 02 H): Starting address of the requested data
is inconsistent with transmittable address from the device.

ILLRGAL DATA VALUE(Exception Code: 03 H): The requested number of data is
inconsistent with the transmittable number of address.

SLAVE DEVICE FAILURE(Exception Code: 04 H): Not properly complete the requested
command.
The example of reading output stauts (ON: 1, OFF: 0) of Coil 001001(03E8 H) which does not
exist on Slave(Address 17) from Master.

Query (Master)
Slave Address Function
Starting Address No. of Points Error Check
(
CRC16)
High Low High Low Low High
11 H 01 H 03 H E8 H 00 H 01 H ## H ## H

Response (Slave)
Slave Address
Function
(
C80
H
Exception Code
Error Check(CRC16)
Low High
11 H 81 H 02 H ## H ## H
CRC16