Deister electronic Logident UDL 250 Wiring And Installation Instructions
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Contents
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5. Interfaces5.1 RS485Most RS485 buses require termination resistors across the conductor pair. The need fortermination has to be checked for each installation. Especially for high data rates, steepedges or long cables termination resistors are absolutely mandatory. Only both ends of themain cable, i.e. at the first and the last device, require termination resistors, additional re -sistors excessively load the drivers. The resistor value matches the cable´s differential modecharacteristic impedance (in most cases 100...120 Ω).Attention!This termination resistor (terminator, 120 Ω) is factory built-in into all UDL250 and has to be deactivated if necessary (see also chapter 9.1.2 “BasicSetup” –> “enable 485 termination” within the configuration menu “Web-Config”). The factory setting of this termination resistor is “on”.At the RS485 bus you need fail-safe biasing containing a pull-up and a pull-down resistoron the cable which are both built-in into the UDL 250. The fail-safe biasing provides aknown state in which there is no active driver on the bus and is therefore absolutelymandatory regardless of data rates and length of cables. The pull-up and pull-down resistorscan only be activated together with the termination resistor (within WebConfig).V14/05/09 896108_wi_en_li_udl-250_pro_v130214_io_sk_fh_bf.odt 9Wiring and Installation UDL 250 |
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