Master and Slave role change on RS-485 bus

[DavidLee]

Hello,

On my 485 bus , there are 25 controllers which use DOS as the OS . If want to take a controller as the master , others are the slave , how to communicate with a specified controller ?

David

[Jattie]

RS 485 devices has to be addressed before they would respond, so anyone on the bus can talk but only the device addressed will reply. The requesting device will be the master polling the slaves for data.

Communicating with these devices still using standard serial procedures and the protocol of the specific devices would normally determine the exact makeup of the serial string transmitted to solicit a response. The serial protocol should be covered in your device product documentation.