Contemporary-control-systems BASgatewayLX Manuale Utente Scaricare il pdf (Pagina 11)

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EIA-485 Bias and Termination Jumpers

After removing the gateway cover, three jumpers are accessible on a 6-pin jumper block

located near the EIA-485 connector. With all jumpers installed (default condition), this

resistor network imparts to the bus approximately 245 mV of bias via the upper jumper

(pull-up) and the lower jumper (pull-down), and 130 Ω of termination impedance with

the middle jumper. With all three jumpers in place, the effective termination resistance

is 120 Ω — consistent with the EIA-485 standard. It is recommended that the gateway

be installed at the end of a segment — but if installed mid-span, remove all the jumpers

and install 120 Ω resistors at each far end of the bus. If no bias source is available for

the bus, apply the gateway’s internal bias by installing the outer jumpers while leaving

the inner jumper location vacant.

Figure 11 — Internal Termination and Bias

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Contemporary-control-systems BASgatewayLX Manuale Utente Pagina 11