from the Project department...
RS485 Modbus, Limitation on Number Of Slaves
Application Questions and Problems topic
Posted by Sagar on 10 November, 2002 - 3:04 pm
Want to know the Theoritical & Practical Mimitation on RS485 Modbus Communication Length & Number OF Slaves a Master Can Handle.

Posted by M. Harisman - Integra Teknik on 11 November, 2002 - 5:25 pm
The limitation will come from the RS-485 network, and not from Modbus protocol run on it.

The maximum Nodes on one RS-485 network is 32. Maximum distance will depend on the applied speed as well as the cable type.

The maximum Modbus Slaves per one multi-drop network is 255.

For complete overview on RS-485 interface, you could visit :
"": pecs.htm
" s/microsys_art_RS485.pdf": ces/images/documents/microsys_art_RS485.pdf

For technical resource on Modbus protocol, you could visit :

M. Harisman harisman(AT)

Posted by Mike McCafferty on 14 November, 2002 - 6:07 pm
For MODBUS, VALID slave addresses are 0-247, where 0 is for broadcast.

The maximum also depends on the PHYSICAL network.

For RS485 networks, depending on the design, a "typical" maximum is 32 nodes, however, with proper design this can be increased. Also, buffer transceivers can be used to extend the network.


Posted by Michael on 27 November, 2002 - 5:27 pm
You may have up to 256 RS-485 nodes with 1/8 impediance transceivers. Many manufactures produce these today (try Maxim or TI).


Your use of this site is subject to the terms and conditions set forth under Legal Notices and the Privacy Policy. Please read those terms and conditions carefully. Subject to the rights expressly reserved to others under Legal Notices, the content of this site and the compilation thereof is © 1999-2014 Nerds in Control, LLC. All rights reserved.

Users of this site are benefiting from open source technologies, including PHP, MySQL and Apache. Be happy.

Radioactive cats have 18 half-lives.