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PR 5610 Installation Manual
Operation with Terminal
Sartorius
101
4.10 MODBUS / J-BUS Protocol
4.10.1 Communication
The MODBUS / J-BUS protocol implemented in PR 5610 permits quick, simple and reliable communication
between a PC or a PLC and max. 127 units.
PR 5610 fully supports Modbus-RTU including functions 1, 2, 3, 4, 5, 6, 8 (subfunction 0), 15 and 16.
J-Bus is a french clone of Modbus. There is only one small difference: J-Bus addresses are counted from 0
(instead of 1) up to hex FFFF (instead of dec. 9999). Some Modbus masters subtract the 1 automatically before
sending a message and some Modbus slaves add 1 to get at the requested address. So it could end up with
accessing an address off by one, but that's the only item to be looked-out for (simple to solve). In practice no
other problems with connecting J-Bus equipment to ordinary Modbus equipment should occur.
The MODBUS / J-BUS protocol is used for data transmission in binary from and to the PR 5610 SPM. Each data
exchange includes two telegrams: a command from the PC to PR 5610 and a reply from PR 5610 to PC.
Command
Command
PC
Reply
Reply
PR
5610
Each telegram comprises four blocks:
1. device address
2. function code
3. data (addresses and values)
4. CRC check word
Note: All 2-byte values (16-bit values/ word) have Motorola notation. Sequence: MSB - LSB
A reply is sent on each faultless command, the answertime amounts to 4ms (typical) and 8 ms (max.) at 9600
baud.
A faulty command received by PR 5610 (e.g. parity error in the data or CRC error) is ignored. In this case, no
reply is sent.
The pauses between the individual characters in a command must not be longer than 3.5 times a character
length. Otherwise, PR 5610 detects an early end of command.
If the received command is faultless, but cannot be handled (e.g. faulty address, faulty data), the reply has got
an error telegram. A telegram to slave 0 is executed by all PR 5610 units, but not replied by anyone.