Editing Modbus (section)

==Limitations==
* Since Modbus was designed in the late 1970s to communicate to programmable logic controllers, the number of data types is limited to those understood by PLCs at the time. Large binary objects are not supported.
* No standard way exists for a node to find the description of a data object, for example, to learn that a register value represents a temperature between 30 and 175 degrees.
* Since Modbus is a client/server (formerly master/slave) protocol,<ref name="x5">{{Cite web |last= |first= |title=Modbus Organization Replaces Master-Slave with Client-Server (press release) |url=https://modbus.org/docs/Client-ServerPR-07-2020-final.docx.pdf |website=modbus.org |date=9 July 2020 |access-date=11 July 2023}}</ref> there is no way for a field device to get data by the event handler mechanism (except over Ethernet TCP/IP, called open-mbus) as the client node must routinely poll each field device and look for changes in the data. This consumes [[bandwidth (computing)|bandwidth]] and network time in applications where bandwidth may be expensive, such as over a low-bit-rate radio link.
* Modbus is restricted to addressing 247 devices on one data link, which limits the number of field devices that may be connected to a parent station (again, Ethernet TCP/IP is an exception).
* Modbus protocol itself provides no security against unauthorized commands or interception of data.<ref>{{cite conference |date=23–25 March 2009 |editor-last=Palmer |editor2-last=Shenoi |editor2-first=Sujeet |title=Critical Infrastructure Protection III |conference=Third IFIP WG 11. 10 International Conference |location=Hanover, New Hampshire |publisher=Springer |page=87 |isbn=978-3-642-04797-8}}</ref>