Optional Grounding Arrangements; Rs-485 Line Failsafe Biasing; Rs-485 Line Termination - Brainboxes ES-357 Product Manual

Optional Grounding Arrangements

Proper operation of the cable circuit, according to TIA EIA: 485 A (1995) requires that the cable
ground shield is not connected directly to the equipment ground shield. A current limiting resistor
should be used in series with the shield to avoid possible large current flow due to differences in
ground potential. Any one of the methods shown below can do this.
The circuit common of the equipment is connected to protective ground, at one point only by a 100 ,
±20% resistor with a power dissipation rating of 1/2W. An additional provision may be made for the
resistor to be bypassed with a strap to connect signal common and protective ground directly together
when specific installation conditions necessitate.
Configuration A
Configuration B

RS-485 Line Failsafe Biasing

Since RS-485 devices have to take turns to send data on the bus there are times when the bus lines
are idle, (not driven by any device) and they float to an indeterminate state generating false data. To
solve this; at each end of the RS-485 bus, add a pull up and a pull down resistor to put the line into a
known, good state during idle times. Brainboxes products have factory fitted bias resistors that are
jumper enabled.

RS-485 Line Termination

Reflections at the end of the twisted pair cable run can interfere with data on the line and so can
cause errors.
Brainboxes products have factory fitted termination resistors that are jumper enabled. Fit the jumper
ONLY if this device is at the end of the cable.
These are the two main wiring schemes:
RS-485 One Talker Many Listeners (Half Duplex)
RS-485 Many Talkers Many Listeners (Half Duplex)
Please see Section 20 for the pin outs of RS-422 and RS-485 for your ES Device.
RS-485 Full Duplex Mode (ES-313, ES-320, ES-346 & ES-842)
Version 2.9
ES Range Product Manual Page 24 of 66
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