Rice Lake PR5220 Ethernet Transmitter - Manual (Page 117)

PR 5220 Instrument Manual J-Bus/ModBus Protocol
Sartorius EN-117
5 J-Bus/ModBus Protocol
5.1 General Description
The J-Bus/ModBus protocol implemented in the instrument permits fast, simple and reliable communication
between a PC or a PLC and up to 127 instruments.
PR 5220 fully supports
-
ModBus-TCP (via network interface), see Chapter 5.2
- ModBus-UDP (via network interface), see Chapter 5.2
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 5220 are transmitted using this protocol. Any data exchange includes
two telegrams: a command from the PC to PR 5220 and a reply from PR 5220 to the PC.
Command Command
PC
Reply Reply
PR 5220
Note:
A telegram sent to Slave 0 is executed by all ModBus users, but not replied by anyone!
2-byte values (16-bit values/word) have the Motorola notation. Consequence: MSB - LSB
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.