Data Sheet

GNM3D and GNM3T Series Communication Protocol
5
Response frame (incorrect action)
Description
Length
Value
Note
Physical address
1 byte
1 to F7h (1 to 247)
Possible exception :
01h: illegal function
02h: illegal data address
03h: illegal data value
04h: slave device failure
Function code
1 byte
86h
Exception code
1 byte
01h, 02h, 03h, 04h
CRC
2 bytes
1.2.4
Function 08h (Diagnostic with sub-function code 00h)
MODBUS function 08h provides a series of tests to check the communication system between a client
(Master) device and a server (Slave), or to check various internal error conditions in a server.
GNM3D Series supports only 0000h sub-function code (Return Query Data). With this sub-function the
data passed in the request data field is to be returned (looped back) in the response. The entire
response message should be identical to the request.
Request
frame
Description
Length
Value
Note
Physical address
1 byte
1 to F7h (1 to 247)
Function code
1 byte
08h
Sub-function
2 bytes
0000h
Data (N word)
N *2 bytes
Data
Byte order: MSB, LSB
CRC
2 bytes
Response frame (correct action)
Description
Length
Value
Note
Physical address
1 byte
1 to F7 (1 to 247)
Function code
1 byte
08h
Sub-function
2 bytes
0000h
Data (N word)
N *2 bytes
Data
Byte order: MSB, LSB
CRC
2 bytes
Respons
e frame (incorrect action)
Description
Length
Value
Note
Physical address
1 byte
1 to F7h (1 to 247)
Possible exception :
01h: illegal function
02h: illegal data address
03h: illegal data value
04h: slave device failure
Function code
1 byte
88h
Exception code
1 byte
01h, 02h, 03h, 04h
CRC
2 bytes
1.2.5
Broadcast mode
In br
oadcast mode the master can send a request (command) to all the slaves. No response is returned
to broadcast requests sent by the master. It is possible to send the broadcast message only with
function code 06h using address 00h.