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how many different kinds of devices can be connected to modbus protocol?

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My question is we have a maximum of 247 slave IDs .


Each Device has some unique slave Id .


In this way  can we connect only 247 different types of devices to the modbus . ?


Can i have some clear explaination please?

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Accepted by topic author mahi108



Modbus is restricted to addressing 247 devices on one data link, which limits the number of field devices that may be connected to a master station.


However, if you want to increase the number of slaves, you may use MODBUS/TCP.

Here is a link that might help you:


The Schneider electric 174CEV30010 Modbus to Ethernet bridge is capable of addressing Modbus slaves from 1 to 247.

The actual number of devices which can be physically connected depends on the medium used and not on the fact it is Modbus.
Some examples:
RS232 is a 2 device point to point connection when using copper, however when using fiber (or other modems) it is possible to connect up to the maximum of 247 devices.

RS485 is multi-drop and supports 32 devices on a single network. When a repeater is used, on copper wire, the number of devices can usually be increased to 64.


Hope this helps.



Rohan Sood
Applications Engineer
National Instruments
Message 2 of 2