Terminating Resistor - Cisco IR829 Hardware Installation Manual

Product Overview
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4 Wire RS485 (Full Duplex)
Characteristics of a 4 wire, or Full Duplex RS485 connection include:
• Bus cable with a max. length of 1200 m (4000 ft) depending upon cable quality and speed of the data
• Stub cable of max. 5 meters
• Master/slave applications
• Inverted line is generally indicated by the index "A" or "-"
• Non-inverted line designated as "B" or "+"
• Except for trivially short point to point connections, terminating resistors are generally required.
• A ground wire is also normally used in addition to what is shown in
Figure 15: 4 Wire RS485 (Full Duplex)
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Wiring Recommendations for RS-485 Networks:
• Typically Category 5 Ethernet cable is suitable for RS-485.
• Shielded cable is desirable and the shield should be grounded at on end if it is used.

Terminating Resistor

RS485 Device
Bus Cable 1200m (4000
ft.)
Duplex), on page 39
Failsafe Bias Resistor
Terminating Resistor
RS485 Master
Bus Cable 1200m (4000
ft.)
Cisco IR829 Industrial Integrated Services Router Hardware Installation Guide
4 Wire RS485 (Full Duplex)
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Figure 15: 4 Wire RS485 (Full
5 Device Cable (Maximum
of 5 m)
RS485 Slave
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39