Impulse 3055 User Manual download pdf (Page 12)

Card Setup

Sealevel Systems ULTRA-485 Page 9

Line Termination

Typically, each end of the RS-485 bus must have line terminating resistors (RS-

422 terminates at the receive end only). A 100-ohm resistor is across each RS-

530/422/485 input in addition to a 1K ohm pull-up/pull-down combination that

biases the receiver inputs. DIP-switch SW2 provides the ability to customize this

interface to system requirements. Each switch position corresponds to a specific

portion of the interface. If multiple ULTRA 485 adapters are configured in a

RS-485 network, only the boards on each end should have switches T, P & P

ON. Refer to the following table for each position’s operation:

Name Function

T Adds or removes the 100 ohm termination.

P Adds or removes the 1K ohm pull-down resistor in the

RS-422/RS-485 receiver circuit (Receive data only).

P Adds or removes the 1K ohm pull-up resistor in the RS-422/RS-

485 receiver circuit (Receive data only).

L Connects the TX+ to RX+ for RS-485 two-wire operation.

L Connects the TX- to RX- for RS-485 two-wire operation.

Figure 8 - SW2, Line Termination

1 2 3 4 5

OFF

T P P L L

1 2 ... 7 8 9 10 11 12 13 14 15 16 17 ... 23 24

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Impulse 3055 User Manual Page 12