Modbus exception responses – Flowserve L75 Series Electric Actuator User Manual
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L75 Series Electric Actuator — Modbus RTU FCD LMAIM7502-00 – 07/05
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the message was broadcast—the command will not be executed. A command contains an illegal field if
any of the following conditions is true:
The message contains a coil address other than 1 or 2.
The message contains a register address other than locations 10001 (coil 1) or 10002 (coil 2).
The message contains force coil data other than 0000 or FF00 hex.
The message contains an incorrect number of points.
The message contains an unimplemented function code.
The message contains a read holding register address other than 40,004 – 40,013
The message contains a register preset value other than 256, 512, or 768 (dec).
Modbus Exception Responses
Exception responses are given when the actuator receives a command message with at least one field
containing an illegal value. In an exception response, the actuator returns the function code byte with
the most significant bit set followed by an exception code byte.
The following exception codes are supported:
Exception
Code
Name
Meaning
01
Illegal Function
The function code received in the query is not supported by the actuator.
02
Illegal Data Address The data address (register or coil address) received is not an allowable
address for the actuator.
03
Illegal Data Value
A value contained in a data field that is not an allowable value for the
actuator. This could include the request of more data points than are allowed
or forced coil data of other than 0000 or FF00 hex.
An exception response message contains the address of the actuator, the function in error, an error code
from the table above and the CRC bytes. The Error Function is the function code byte with the most
significant bit set. The fields of an exception message are shown below:
Command issued by host:
Field Name
Example
Actuator Address
05
Function (Read Coil Status)
01
Starting Address (High)
00
Starting Address (Low)
06 (Illegal Address)
Number of Points (High)
00
Number of Points (Low)
01
CRC Error Check (LS byte)
1C
CRC Error Check (MS byte)
4F
1.
2.
3.
4.
5.
6.
7.
Response from the actuator:
Field Name
Example
Actuator Address
05
Error Function (Read Coil Status)
81
Exception Code (Illegal Data Address)
02
CRC Error Check (LS byte)
80
CRC Error Check (MS byte)
50