Max number of clients/slaves of Connect over RS485?

[ulf]

Hi,

I have tried to find in the docs or forum if there is a mention of how many daisy-chained RTU Modbus slaves the Connect models can cope with, but I have not seen any definitive number anywhere.

In particular, we are looking to use the Connect S as an RS485 Modbus master over /dev/ttyRS485 for a project which might require more than 32 slaves, and we'd like to confirm if this is possible.

Many thanks.

[dirk]

Hello Ulf, well, the maximum addressable Modbus-RTU Servers are 247
https://en.wikipedia.org/wiki/Modbus#:~ ... %20address.

But your idea is right per RS485 segment there may be a limitation to 32 devices on a serial line because of the serial driver.

[ulf]

Thank you, Dirk,

It's very encouraging to know that the Revolution Pi RS485 aligns with Wikipedia on RS485; but yes, it sounds like it will be a good idea not to promise more than 32 slaves for any one master without proper testing.

Many thanks,
Ulf

[dirk]

Hello ulf,
take a look here to this output - it is the modpoll tool.

Modpoll

[ulf]

Thank you, Dirk,

yes, this is a good clue indeed - we'll keep an open mind how many RS485 modbus slaves we can support but make sure we test thoroughly before deployment!