Commad Code 0X08Diagnostic Function; Respond Pdu; Wrong Pdu - Danfoss VFD500 Series Manual

VFD500 high performance vector control frequency inverter user manualAppendix A
Initial address
Number of register

Wrong PDU

●
Command code
Abnomal Code
A.3.4 Commad code 0x08Diagnostic function
Modbus Command Code 0x08 Providea series of tests to check the communication system
●
between the client (master) device and the server (slave) or various internal error conditions in
the server.
This function uses the sub-command code of 2 bytes inquery to define the type of test to be
●
performed. The server copies the command and subcommand codes in the normal response.
Some diagnostics cause the remote device to return the data through the normally responding
data fields.
● Diagnostic functions to remote devices generally do not affect the user program running in the
device. The main diagnostic function of this product is not line diagnosis (0000), used to test the
host from the machine is normal communication.
Request PDU
●
Command code
Subcommand code

Respond PDU

Command code
Subcommand code
Wrong PDU
Command code
Abnomal code
A.4 Abnormal response information
When the master device sends a request to the slave device, the master expects a
normal response. The master's query may result in one of four events:
(1) If the slave device receives a request for a communication error and the query can
be processed normally, the slave device will return a normal response.
(2) If the slave device does not receive the request due to a communication error, no
information can be returned and the slave device times out.
(3) If the slave device receives a request and detects a communication error (parity,
address, framing error, etc.), no response is returned and the slave device times out.
(4) If the slave device receives no communication error request, but can not handle the
request (such as the register address does not exist, etc.), the slave station will return
an abnormal response to inform the master of the actual situation.
Abnormal response command code = normal response command code + 0x80,
Abnormal code value and meaning as shown in the following table
Error
code
0x01 Invalid command code/error
Data
Data
Name
function code
Modbus communication protocol
2byte
0x0000～0xFFFF( high 8
bit in front)
2byte
1～16(1～16, high 8 bit
in front)
1byte 0x90
1byte See Abnormal response
information
1byte 0x08
2byte
0x0000～0xFFFF
2byte
0x0000～0xFFFF
1byte 0x08
2byte 0x0000
2byte Same as request of PDU
1byte 0x88
1byte See Abnormal response
information
Description
The function code received by the slave is outside the
configured range
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