Editing Modbus (section)

===JBUS mapping===
Another ''de facto'' protocol closely related to Modbus appeared later, and was defined by [[Programmable logic controller|PLC]] maker April Automates, the result of a collaborative effort between French companies [[Renault]] Automation and [[Merlin Gerin]] et Cie in 1985: JBUS. Differences between Modbus and JBUS at that time (number of entities, server stations) are now irrelevant as this protocol almost disappeared with the April PLC series, which AEG Schneider Automation bought in 1994 and then made obsolete. However, the name JBUS has survived to some extent.

JBUS supports function codes 1, 2, 3, 4, 5, 6, 15, and 16 and thus all the entities described above, although numbering is different:
* Number and address coincide: entity #''x'' has address ''x'' in the data frame.
* Consequently, entity number does not include the entity type. For example, holding register #40010 in Modbus will be holding register #9, at address 9 in JBUS.
* Number 0 (and thus address 0) is not supported. The server should not implement any real data at this number and address, and it can return a null value or throw an error when requested.