Sartorius X3 PR 5410, Operating Manual

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Commissioning X3 Operating Manual
108 Sartorius
4.12 MODBUS / J-BUS Protocol
4.12.1 Communication
The MODBUS/J-BUS protocol implemented in the instrument permits fast, simple and reliable
communication between a PC or a PLC and up to 127 instruments. PR 5410 fully supports Modbus-RTU
including functions 1, 2, 3, 4, 5, 6, 8 (sub-function 0), 15 and 16.
J-bus is a French 'clone' of the Modbus. There is a small difference: J-bus addresses count from 0 (instead
of 1) to hex FFFF (instead of dec. 9999). Some Modbus masters automatically subtract 1 before sending a
message, and some Modbus slaves subtract 1 to get the requested address. Thus it may happen that access
to an address shifted by 1 is made; this is the only point which must be taken into account. In everyday
practice, no other problems when connecting J-bus and Modbus instruments should appear.
Binary data from and to the SPM of PR 5410 are transmitted using this protocol. Any data exchange
includes two telegrams: a command from the PC to PR 5410 and a reply from PR 5410 to the PC.
Command Command
PC
Reply Reply
PR 5410
Each telegram consists of four blocks:
1. Device address
2. Functional code
3. Data (addresses and values)
4. Control word (CRC)
Note: All 2-byte values (16-bit values/word) have the Motorola notation. Consequence: MSB - LSB
A reply to every correct command is sent. At 9600 bauds, the reply time is typical 4 ms and maximal 8 ms.
A faulty command received by PR 5410 (e.g., parity error in the data, or CRC error) is ignored and no reply is
sent.
The pauses between the individual characters and a command must not exceed the 3.5-fold value of a
character length; otherwise PR 5410 detects a premature end of the command.
If the received command is correct but cannot be executed nevertheless (e.g. due to a faulty address or
faulty data), reply is with an error telegram.
A telegram sent to Slave 0 is executed by all PR 5410 units, but not replied by anyone.