Bioscrypt Inc. 4GCRP Manual Do Utilizador
Part # 430-4G-050-00-004
© 2011 - L-1 Identity Solutions Inc. All rights reserved
© 2011 - L-1 Identity Solutions Inc. All rights reserved
Planning the Installation
2.1.6.1.1 RS-485 CABLE SPECIFICATION
4G V-Series 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 RS-485
communications. The cable connection includes a differential line (A and B) and a GND
connection.
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 RS-485
communications. The cable connection includes a differential line (A and B) and a GND
connection.
Table 2-2 Category 5 Cable Characteristics
Specification
Recommendation
Capacitance (conductor to conductor)
<20 pF/ft.
Characteristic Impedance
100 - 120 ohms
Nominal DC resistance
<100 ohms/1000 ft.
Wire gauge
24 AWG stranded
Conductors/Shielding
>2 pair (shielding is recommended)
2.1.6.1.2 RS-485 CABLE LENGTHS
As outlined in the RS-485 specification, the total length of the communication cable (adding
up all of the segments of the run) should not exceed 1200 meters (4000 feet). Although the
RS-485 specification calls for a maximum cable length of 1200 meters and provides a
maximum baud rate well above that of the 4G device, a more conservative system should be
configured to no more than 1000 meters and run at a baud rate of 9600 bits per second. After
the network is configured and is running in a stable manner, the baud rate can be increased if
faster network communications are desired.
up all of the segments of the run) should not exceed 1200 meters (4000 feet). Although the
RS-485 specification calls for a maximum cable length of 1200 meters and provides a
maximum baud rate well above that of the 4G device, a more conservative system should be
configured to no more than 1000 meters and run at a baud rate of 9600 bits per second. After
the network is configured and is running in a stable manner, the baud rate can be increased if
faster network communications are desired.
Drops (down-leads, stubs, T-connections, etc.) to equipment are not recommended, but if
required, should not exceed one foot) and should use the same cable recommended above.
On a long stub, a signal that travels down the wire reflects to the main line after hitting the
input impedance of the device at the end. This impedance is high compared with that of the
cable and the net effect is degradation of signal quality on the bus.
required, should not exceed one foot) and should use the same cable recommended above.
On a long stub, a signal that travels down the wire reflects to the main line after hitting the
input impedance of the device at the end. This impedance is high compared with that of the
cable and the net effect is degradation of signal quality on the bus.
2.1.6.1.3 RS-485 NETWORK TOPOLOGY
Communication cables for RS-485 should be laid out in a daisy chain configuration (See
Figure 2-3). Long stubs or drop downs and the star configuration should be avoided because
they create discontinuities and degrade signal quality. The star configuration usually does not
provide a clean signaling environment even if the cable runs are all of equal length. The star
configuration also presents a termination problem, because terminating every endpoint
overloads the driver. Terminating only two endpoints solves the loading problem, but creates
Figure 2-3). Long stubs or drop downs and the star configuration should be avoided because
they create discontinuities and degrade signal quality. The star configuration usually does not
provide a clean signaling environment even if the cable runs are all of equal length. The star
configuration also presents a termination problem, because terminating every endpoint
overloads the driver. Terminating only two endpoints solves the loading problem, but creates
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