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LNL-2000 Intelligent System Controller
Port 6 may be set up as RS-232 interface or a RS-485 interface. RS-485 interface may be 2-wire or 4-wire
type.
Direct-connect RS-232 cables should be no longer than 50 feet. Leased lines or fiber optics can also be used.
RS-232 Communications
The RS-232 communications interface is for short distance wiring or point to point communications. A
number of products provide RS-232 interfaces such as connections to modem, PC, etc. This interface is
intended for a short distance communication because its high impedance is more susceptible to noise. Cable
length is generally limited to 50 feet (15.24 m). If required, this distance may be extended to a few hundred
feet by using low capacitance shielded cables. The optimal cable is a (Belden 9610) or equivalent wire.
For direct connections (via RS-232) between the LNL-2000 and the host, 115,200 baud is not recommended
unless the third-party hardware devices used support a CTS/RTS hardware handshake at the UART level.
The Microsoft serial device drivers do not support hardware handshaking at this level. The 115,200 baud
rate can be used for the RS-232 connection between the LNL-2000 and the Lantronix devices that support
115,200 baud.
RS-485 Communications
The (EIA) Electronic Industries Association standard defines RS-485 as an electrical interface for multi-port
communications on a bus transmission line. It allows for high-speed data transfer over extended distance
(4000 feet/1219 m). The RS-485 interface uses a balance of differential transmitter/receiver to reject
common mode noise. For increased reliability over the extended distances End-of-line (EOL) termination is
required.
RS-485 communication requires a 24 AWG (minimum) twisted pair (with shields) cable. Either a 2-wire or
4-wire RS-485 cable configuration can be used. The RS-485 cable should be no longer than 4000 feet (1219
m), 100 ohms minimum impedance (Belden 9842 4-wire or 9841 2-wire, plenum cabling Belden 88102,
West Penn, or equivalent). Install a termination jumper only for end of line unit(s).
When connecting to the host via RS-485 (2-wire or 4-wire), do not use the 115,200 baud rate because there
is no hardware handshake capability. For reliable communication with this baud rate, CTS on the host must
be connected to RTS on the controller; RS-485 communication does not provide this.
When connecting a controller to a Lantronix device, do not use RS-485 communication. This particular
configuration also lacks hardware handshake signals. RTS on the Lantronix must be connected to CTS on
the controller. At 115,200 baud, CTS on the Lantronix must be connected to RTS on the controller as well,
which is not provided via RS-485.
RS-485 Line Termination
RS-485 (2-wire or 4-wire) must be terminated at both ends of the RS-485 line (bus). Terminating the line
provides a more reliable communication by minimizing the signal reflection and external noise coupling.
98 —
revision 7
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