Emerson OpenComms-485 Manuel D’Utilisation

 

REV. 5 

 7/6/2007

 

Liebert Monitoring Group –Development 

 

1 

 

This design specification describes the Modbus communications protocol as 
supported by the OC-485 interface card.  It includes information on how to pass 
information to and from the OC-485 card via Modbus.  It is also intended to help 
facilitate answering questions regarding supported types, frame format, function 
code support etc. 

Implementation Basics 

Protocol controls the language structure or message format between devices in 
other words, the rules for communication.  The rules for communication include 
how master and slave devices initiate communications, as well as unit 
identification, message handling and error checking.  Modbus protocol simply 
refers to the control of the query and response cycles between master and slave 
devices. 
The OC-485 card is configured to act as a slave device on a common network.  
This common network can be a multi-drop configuration over EIA-485, where 
multiple slaves reside on a common wire or loop. 

Transmission Format 

The OC-485 interface card supports Modbus RTU (Remote Terminal Unit) 
transmission modes.  .  See chart below. 
 

EIA-

485/422 

2 wire 

RTU 9600, 

19200 

or 38400 

Configurable Configurable Configurable  No