What speed and distance can reach Modbus?

Thanks a lot.

Juan Carlos Vásquez
Techvalue Peru SAC
Sales Engineer - Industrial Networking
Gomez del Carpio 160
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Modbus is a protocol. A protocol is a set of rules that defines
- the format of messages
- what kind of messages are acceptable or not
- who talks when and to whom,
- who listens when and to whom,
- how to whom responses are sent
- how to define errors and deal with errors.

The physical layer defines how far a signal goes, not the protocol. Typical physical layers for Modbus are RS-232, RS-485, ethernet, 232 over phone modems.

Generally, RS-232 is good to 5-10 meters (?).
RS-485 can go 1000 meters, but experience shows that the baud rate affects distance, the slower the baud rate, the longer the distance to maintain reliability.

Sometimes RS-232 runs over a telephone modem. What's the distance limitation of a telephone link? Depends . . . .

Modbus TCP is Modbus over ethernet. Ethernet is spec'd to 100m point to point, but fiber cable can go much longer distances.

Low power (1W), 900Mhz wireless can go 20Km.

 

Anonymous wrote: > Modbus TCP is Modbus over ethernet. Ethernet is spec'd to 100m point to point, but fiber cable can go much longer distances. <

That was a VERY good post until you got to there. Modbus/TCP is an IP protocol subset. IP works on many physical layers, Ethernet is just one of them. Modbus/TCP will go as far as the IP packet that envelopes it will allow.