Modbus Exception Response Telegrams
Under some circumstances, the drive may reply with an Exception Response (error) in response to a request
telegram sent from the network master, for example where the master tries to read a register which does not
exist. Exception Responses which can be generated by the drive are listed below:-
Exception Code 1: Invalid Request
Returned under the following conditions
- Network Master sends an unsupported Modbus command (e.g. Read Coils).
- Run command issued to drive whilst the drive is not set for Modbus Control Mode (P-12 <>3 or 4).
- Run command issued to drives whilst the drive is not enabled (e.g. Digital Input 1 is open).
- Run command issued to drive whilst the drive is in a tripped condition.
Exception Code 2: Invalid Modbus register
Returned under the following conditions
- Network Master attempts to read or write a register that does not exist within the drive.
Exception Code 3: Register Value Out of Range
Returned under the following conditions
- Network Master attempts to write a holding register with a value outside the range of the register
Exception Code 6: Drive Busy
Returned under the following conditions
- Drive busy due to internal data transfer. The Network Master should re-send the message after a delay
Dataflow example:
Read data from register 6
Request:[01] [03] [00] [05] [00] [01] [94] [0B]
(Drive Addr) (Command) (Reg start addr) (No. of Registers) (Checksum)
Reply: [01] [03] [02] [00] [00] [B8] [44]
(Drive Addr) (Command) (No of data bytes) (Data) (Checksum)
Note: The actual start address of register 6 is 5. All data in [ ] is in 8bits Hex format.
Write start command to the register 1 (suppose P-12 = 3, P-15 =0 and digital input 1 is closed):
Request: [01] [06] [00] [00] [00] [01] [48] [0A]
(Drive Addr) (Command) (Reg addr) (Data value) (Checksum)
Reply: [01] [06] [00] [00] [00] [01] [48] [0A]
(Drive Addr) (Command) (Reg addr) (Data value) (Checksum)
Note: The actual address of register 1 on the data link is 0. All data in [ ] is in 8bits Hex format.
Reply can be error message depending on drive parameter settings and digital input status.
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