RS-485 Protocol


Thread Starter


Can anyone give me some help about the standard protocols for use on an
RS-485 based network. I have developed an 32 Units Network with half
duplex comm., but don't know any protocol for use with it.

Assuming you want a protocol which any potential customer would not
object to - ie: widest possible sales, then just use Modbus/RTU.

Modbus is NOT perfect, but it is easy to do and 99% of all
non-proprietary computer applications can easily talk to it. See the
spec at .

If you want something which allow simple peer-to-peer messages, then
Allen-Bradley's DF1 (see half-duplex allows a master device
to poll slaves and also move messages between slaves. It is also widely
used by computer applications, but a little more complicated to do.

Best Regards

Lynn August Linse, Senior Product Application Engineer
15353 Barranca Parkway, Lantronix Inc, Irvine CA 92618
[email protected]
Tel: (949)450-7272 Fax: (949)453-7132
Hello Gustavo,

You could basically use any protocol you wish over the EIA-485 physical layer. However, Modbus is a very common protocol used over 485 and the protocol specification is in the public domain.


Gord Ellis, P. Eng.
Principal, Northern Dynamic Inc.
J103-155 Frobisher Drive
Waterloo, Ontario
Canada N2V 2E1
Tel/Fax: (519) 725-2071/2072