BECKHOFF BK7300 - Manual (Page 24)

MODBUS
20 BK7300
Read Digital Outputs (Function 1)
READ COIL STATUS Function 1 can be used to read the settings of the digital outputs.
In this example the first 10 digital outputs of slave number 11 are read. The
start address is zero. If an offset is to be entered, this is done in the "Start
address" field.
Query
Byte Name Example RTU ASCII
Start frame „:“ 0x3A
Slave address 11 0x0B „0B“ 0x30, 0x42
Function code 1 0x01 „01“ 0x30, 0x31
Start address high 0 0x00 „00“ 0x30, 0x30
Start address low 0 0x00 „00“ 0x30, 0x30
Count high 0 0x00 „00“ 0x30, 0x30
Count low 10 0x0A „10“ 0x31, 0x30
Error Check
LRC / CRC
0xBC
0xA7 „E4“ 0x45, 0x34
End of frame t1-t2-t3 CRLF 0xD, 0xA
Response
The coupler answers with byte count 2, i.e. 2 bytes of data are returned.
The request was for 10 bits, and these are now distributed over 2 bytes.
The third bit in the output process image of the BK7300 is set, and the
coupler returns a "4" in the first data byte.
Byte Name Example RTU ASCII
Start frame „:“ 0x3A
Slave address 11 0x0B „0B“ 0x30, 0x42
Function code 1 0x01 „01“ 0x30, 0x31
Byte Count 2 0x02 „02“ 0x30, 0x32
Data bits 0..7 4 0x04 „04“ 0x30, 0x34
Data bits 8..15 0 0x00 „00“ 0x30, 0x30
Error Check
LRC / CRC
0x23
0x3D „EE“ 0x45, 0x45
End of frame t1-t2-t3 CRLF 0xD, 0xA