Indirect serial (terminal server) connections
You can connect controllers to the network through a terminal server. (A terminal server
allows you to connect several controllers to the network even though they only have serial or
parallel ports.) Most terminal servers also provide a range of serial connection options, such as
RS-232, RS-422 and RS-485.
Tip:
Be aware of the difference between the similar sounding terms 'Terminal Servers'
and 'Terminal Services'. They are quite different terms referring to different
technologies and are not interchangeable.
A Terminal Server is a hardware device for connecting one or more serial
communication controllers (terminals) with an Ethernet network.
Windows Terminal Services (now known as Remote Desktop Services) refers to
software which provides remote desktop connection of Windows-based
computers over a network.
Terminal servers are particularly useful if you have a:
n
Plant-wide LAN, and you want to connect controllers to the LAN—as shown in the
following figure.
n
Geographically-dispersed controllers on a WAN.
Controllers
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