RS232 - Interface
BC8050 und BC815068 Version: 3.0.0
6.1.1.5.3 Function 4: READ INPUT REGISTERS
The READ INPUT REGISTERS function reads the analog inputs.
In this example the first two analog inputs of slave number 11 are read. The analog outputs start at an offset
of 0x0000. The length indicates the number of words to be read. A KL3002 has 2 words of input data, which
is why the value to be entered in "Count low" is two.
Query
Byte Name Modbus RTU Modbus ASCII
Start - frame - - ":" 0x3A
Address 11 0x0B "0B" 0x30, 0x42
Function code 4 0x04 "04" 0x30, 0x34
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 2 0x02 "02" 0x30, 0x32
Error check, LRC/
CRC
0x71, 0x61 "EF" 0x45, 0x46
End - frame t1-t2-t3 CRLF 0x0D, 0x0A
The Fieldbus Box Coupler Box responds with byte count 4, i.e. 4bytes of data are returned. The query was
for 2 analog channels, and these will now be distributed over 2 words. In the analog input process image, the
first channel has the value 0x0038, while the second channel has the value 0x3F1B.
Response
Byte Name Modbus RTU Modbus ASCII
Start - frame - - ":" 0x3A
Address 11 0x0B "0B" 0x30, 0x42
Function code 4 0x04 "04" 0x30, 0x34
Byte Count 4 0x04 "04" 0x30, 0x34
Data 1 high byte 0 0x00 "00" 0x30, 0x30
Data 1 low byte 56 0x38 "38" 0x33, 0x38
Data 2 high byte 63 0x3F "3F" 0x33, 0x46
Data 2 low byte 11 0x0B "0B" 0x30, 0x42
Error check, LRC/
CRC
0x80, 0x7E "6A" 0x36, 0x41
End - frame t1-t2-t3 CRLF 0x0D, 0x0A
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