BONFIGLIOLI Vectron Agile, Communications Manual

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Modbus Agile 37 02/2011
Protocol
7.3.8 Exception Responses
When the master device sends a request to the inverter it expects a normal response. One of four
possible events can occur from the master’s query:
− If the inverter receives the request without a communication error and can handle the query nor-
mally, it returns a normal response.
− If the inverter does not receive the request due to a communication error, no response is returned.
The master will eventually process a timeout condition for the request.
− If the inverter receives the request, but detects a communication error (parity, LRC, CRC, ...), no
response is returned. The master will eventually process a timeout condition for the request.
− If the inverter receives the request without a communication error, but cannot handle it (for exam-
ple, if the request is to read an unknown parameter), the inverter will return an exception re-
sponse informing the client of the nature of the error.
The exception response message has two fields that differentiate it from a normal response:
Function Code Field:
In a normal response, the inverter echoes the function code of the original request in the function
code field of the response. All function codes have a most–significant bit (MSB) of 0 (their values are
all below 0x80 hexadecimal). In an exception response, the inverter sets the MSB of the function code
to 1. This makes the function code value in an exception response exactly 0x80 hexadecimal higher
than the value would be for a normal response. With the function code’s MSB set, the master can
recognize the exception response and can examine the data field for the exception code.
Data Field:
In a normal response, the inverter may return data or statistics in the data field (any information that
was requested in the request). In an exception response, the inverter returns an exception code in the
data field. This defines the server condition that caused the exception.
The Exception Codes generated by the inverter are listed in Chapter 7.3.9 "Exception Codes".
7.3.9 Exception Codes
The following exception codes are generated by the inverter:
Code Modbus Name Cases when generated by the Inverter
1 ILLEGAL FUNCTION
− Function Code unknown
− Subfunction Code unknown (Diagnostics Function)
2 ILLEGAL DATA
ADDRESS
− No. of Registers field incorrect (must always be 0x01)
− Unknown Parameter or Parameter Data Type mismatch
3 ILLEGAL DATA VALUE
− Error in dataset of frame
− No. of bytes too small or too large
− Certain fields not set to specific values
4 SLAVE DEVICE FAILURE
− Read or Write Parameter failed
The reason for the error can be obtained by reading out Parameter
VABusSST Error Register
11.
VABusSST Error Register
11
Error number Meaning
0 no error
1 inadmissible parameter value
2 inadmissible data set
3 parameter not readable (write-only)
4 parameter not writable (read-only)
5 read error EEPROM
6 write error EEPROM
7 checksum error EEPROM
8 parameter cannot be written while the drive is running
9 values of the data sets differ from one another
10 wrong parameter type
11 unknown parameter
12 checksum error in received message
13 syntax error in received message
14 data type of parameter does not correspond to the number of bytes in the mes-
sage
15 unknown error
When the error register
VABus SST Error Register
11 is read out, it is automatically cleared at the
same time.
7.3.10 Modbus Transmission Modes
Two different serial transmission modes are defined: the RTU mode and the ASCII mode. They
define the bit contents of message fields transmitted serially on the line. They determine how infor-
mation is packed into the message fields and decoded.
The transmission mode (and serial port parameters) must be the same for all devices on a MODBUS
Serial Line.
The transmission mode for the Modbus-Communication can be selected via Parameter
Modbus Mode
1503. See Chapter 6 "Modbus".
7.3.10.1 RTU Transmission
When devices communicate on a MODBUS serial line using the RTU (Remote Terminal Unit) mode,
each 8–bit byte in a message contains two 4–bit hexadecimal characters.
The main advantage of this mode is that its greater character density allows better data throughput
than ASCII mode for the same baud rate. Each message must be transmitted in a continuous stream
of characters.
7.3.10.1.1 Character Format
One character consists of 11 bits.
− 1 start bit
− 8 data bits, least significant bit sent first
− 1 parity bit
− 1 stop bit
Note:
If no parity is used then an extra stop bit is added.
Character format with parity checking:
Start B1 B2 B3 B4 B5 B6 B7 B8 Parity Stop
Character format without parity checking:
Start B1 B2 B3 B4 B5 B6 B7 B8 Stop Stop