BECKHOFF BK7300 - Manual (Page 33)

MODBUS
BK7300 29
Byte Name Example RTU ASCII
Start frame „:“ 0x3A
Slave address 11 0x0B „0B“ 0x30, 0x42
Function code 23 0x17 „17“ 0x31, 0x37
Byte Count 4 0x04 „04“ 0x30, 0x34
Data 1 high 0 0x00 „00“ 0x30, 0x30
Data 1 low 56 0x38 „38“ 0x33, 0x38
Data 2 high 63 0x3F „3F“ 0x33, 0x46
Data 2 low 11 0x0B „0B“ 0x30, 0x42
Error Check
LRC / CRC
0x82
0xDD „58“ 0x35, 0x38
End of frame t1-t2-t3 CRLF 0xD, 0xA
Diagnostics
In the Modbus, function 08 provides a series of tests for examination of the
communication system between the master and the slave and for
inspection of a variety of internal error states within the slave. A broadcast
telegram is not supported.
The function uses a two-byte sub-function code field in the query to define
the test that is to be carried out. The slave outputs the function code and
the sub-function code as an answer.
The diagnostic queries use a two-byte data field to send diagnostics data
or control information to the slave.
EXAMPLE Query
Byte Name Example RTU ASCII
Start frame „:“ 0x3A
Slave address 11 0x0B „0B“ 0x30, 0x42
Function code 8 0x08 „08“ 0x30, 0x38
Subfunction high 0 0x00 „00“ 0x30, 0x30
Subfunction low 0 0x00 „00“ 0x30, 0x30
Data high 2 0x02 „02“ 0x30, 0x32
Data low 3 0x03 „03“ 0x30, 0x33
Error Check
LRC / CRC
0xA1
0xC0 „E8“ 0x45, 0x38
End of frame t1-t2-t3 CRLF 0xD, 0xA
Response
Byte Name Example RTU ASCII
Start frame „:“ 0x3A
Slave address 11 0x0B „0B“ 0x30, 0x42
Function code 8 0x08 „08“ 0x30, 0x38
Subfunction high 0 0x00 „00“ 0x30, 0x30
Subfunction low 0 0x00 „00“ 0x30, 0x30
Data high 2 0x02 „02“ 0x30, 0x32
Data low 3 0x03 „03“ 0x30, 0x33
Error Check
LRC / CRC
0xA1
0xC0 „E8“ 0x45, 0x38
End of frame t1-t2-t3 CRLF 0xD, 0xA
Echoes a query (Sub-Function 0)
Sub-function 0 causes the data that is sent to the slave by the master to be
returned.