Transmission Format; Physical Connection - Liebert OpenComms Installation & User Manual

delay time if HTTP, SNMP and Modbus are going to be utilized
simultaneously.

TRANSMISSION FORMAT

The OpenComms NIC module supports Modbus RTU (Remote
Terminal Unit) transmission modes. The OpenComms NIC
communication rate is fixed at 9600 baud, 8 data bits, No
parity, 1 Stop bit. The communication media is fixed using
EIA-485 standards.

PHYSICAL CONNECTION

A Modbus network should consist of one, and only one, host
client, and up to 255 slaves uniquely identifiable by their slave
ID. The slave ID of each OpenComms NIC is set through the
service terminal (configuration) port. (See section 3, System
Configuartion for more details.) The OpenComms NIC supports
multi-drop connection over RS485. On the OpenComms NIC, a
client should connect to the OpenComms NIC as a multi-drop
connection via the RS485 "Repeater" port (TB2), (Pin1 as minus
and Pin2 as plus. J28-1 and J28-2 should be shorted.)
The OpenComms NIC card is designed to reside on a maximum
common line of 32 devices with a total cable length of 4000 feet.
In a "normal environment" all devices should be connected in
"daisy-chain" fashion, with "star configurations" or branches,
being used at a minimum. See Figure 9 for details. A "normal
environment" consists of an installation where noise or electrical
interference is minimal. This is typical of communication wiring
run in properly grounded conduit or in areas where high voltage
or radio transmissions are not present. Otherwise, these
conditions are designated as "noisy."
NIC Setup and Testing
29