Function 3 or 4: reading n successive words, Pr 5230 instrument manual j-bus/modbus protocol – Rice Lake PR5230 Fieldbus Transmitter User Manual
Page 171
PR 5230 Instrument Manual
J-Bus/ModBus Protocol
Sartorius
EN-171
Function 3 or 4: Reading n Successive Words
Command
Device
address
Function
number
Address of
1st word
Number of
words
1 byte
1 byte
2 bytes
2 bytes
Range
1...127
3, 4
0...63
1...64
Reply
Device
address
Function
number
Number of
bytes
Value of the
words
1 byte
1 byte
1 byte
n bytes
MSB
LSB
MSB
- - - - - -
MSB
LSB
1
st
word
last word
If the address of one of the words to be read is out of the permissible range (0...63), an error message is sent as
a reply (the address plus the number of bytes must not exceed 64).
Example of function 3 for reading a gross weight (D8 = W16) of 893 kg with ModBus-RTU:
Command
1
3
0
16
0
2
CRC CRC
Reply
1
3
4
0
0
3
125 CRC CRC
Example with ModBus-TCP:
Command
47
12
0
0
0
6
0
3
0
16
0
2
Reply
47
12
0
0
0
7
0
3
4
0
0
3
125
The individual bytes are shown.