Maximun nodes of Modbus

K

Thread Starter

Kevin Fan

I am working on an automation system architecture and need to know the maximum nodes and cycle time of Modbus TCP and Modbus RTU on RS485.
 
P

Patrick Lansdorf

Hi Kevin,

I guess that for Modbus TCP there is no real limit of nodes. If the subnet mask 255.225.255.0, then it's 254. But you could extend the mask to 255.255.0.0 and get 254x254 nodes. Usually, it will be your hardware that will set the limitation.

For RS485 Modbus RTU, the limitation is 32 nodes (1 master + 31 slaves).

The cycle times depends on a number of things, in my experience the response time of the slave is a main factor. I have an excel sheet for calculating line time for Modbus RTU, let me know if you would like me to send it to you.

Patrick Lansdorf
 
Top