Intelligent RS-485 and RS-422 Adaptors
5
Network Expansion
Provided the cabling is correctly installed and terminated, RS-422 and
RS-485 networks allow a maximum total cable length of 1200 metres,
and can support a maximum load of 31 units plus the RS-422 or RS-
485 adaptor per network. The easiest method of allowing more than 31
units is to split the network into multiple sections, and run each section
from its own adaptor on different serial ports on a single PC. Typical
PC’s have two serial ports, and multiple serial port expansion boards
are available that provide two, four or eight additional serial ports.
Remember that each section of the network can be up to 1200 metres
long, and can support up to 31 units.
Although we have had some users connect more than 31 units together
in a single network without experiencing any problems, we do not
recommend doing so.
The Main Cabling Points Again!
•
The cable
must
be shielded twisted-pair computer data cable.
•
The twisted pairs of wire in the cable
must
be used as pairs.
•
The cable
must
be installed in one continuous run - no joins,
junctions, taps or “T” connections are allowed.
•
The shield
must
be continuous, and connected to ground pins on the
adaptor and each unit.
•
The cable
must
be terminated at each end.
Provided you follow these instructions, you should have no problems
running an RS-485 or RS-422 network up to the maximum of 1200
metres and 31 units.
