Rice Lake PR5230 Fieldbus Transmitter - 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.