User's Manual

October 15 2009 – Installation Guide Draft – Edit Purposes Only Page 28
Installation Guide –April 2010
2010
Spec RS-485 RS-232 100BaseT
Mode of Operation Differential DC Coupled Single-ended DC Coupled Multi
DC Isolation No No No
Maximum Distance 4000 feet 150 feet 330 feet
Number of Devices
on one line
31 1 Unlimited
Maximum Data Rate 56 Kbps
(recommended)
56 Kbps* (recommended) Auto-
negotiated
2.1.6.1 RS-232
If your system has only one device, or a few devices (each only a short distance away
from the SecureAdmin PC) then RS-232 can be used, provided that each device can
have a dedicated RS-232 port.
With RS-232 at 9600 baud, a distance of 150 feet is possible with shielded cable, but at
56 Kbps, a maximum of only 20 feet is recommended.
2.1.6.2 RS-485
RS-485 has two distinct advantages over the more common RS-232. First, it allows you
to connect up to 31 4G devices to a PC with an external RS-232 to RS-485 converter
(available from L-1 Identity Solutions). Second, the RS-485 specification allows for
cable
run lengths up to 4000 feet (1200 meters) at modest baud rates.
An RS-485 network is required instead of RS-232 if:
 Multiple devices must be connected together so that templates can be
distributed among the devices
 The installation has only a single device, but it is over 150 feet (45
meters) from the host PC.
2.1.6.2.1 RS-485 CABLE SPECIFICATION
V-Station 4G devices provide a 2-wire, half-duplex RS-485 interface. The main cable
run should be low capacitance, twisted-pair cable, with approximately 120 -ohm
characteristic impedance. Category-5 rated communications cable is used in RS-485
networks and its characteristics are defined below. This is the recommended cabling for