Omega Engineering RS-422/485 用户手册
Card Setup
OMG-ULTRA-COMM422
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 120-ohm resistor is across each
RS-530/422/485 input in addition to a 1K ohm pull-up/pull-down combination that
bias the receiver inputs. Headers J1E through J4E allow the user to customize this
interface to their specific requirements. Each jumper position corresponds to a
specific portion of the interface. If multiple OMG-ULTRA-COMM422 adapters
are configured in an RS-485 network, only the boards on each end should have
jumpers T, P & P ON. Refer to the following table for each position’s operation:
(RS-422 terminates at the receive end only). A 120-ohm resistor is across each
RS-530/422/485 input in addition to a 1K ohm pull-up/pull-down combination that
bias the receiver inputs. Headers J1E through J4E allow the user to customize this
interface to their specific requirements. Each jumper position corresponds to a
specific portion of the interface. If multiple OMG-ULTRA-COMM422 adapters
are configured in an RS-485 network, only the boards on each end should have
jumpers T, P & P ON. Refer to the following table for each position’s operation:
Name
Function
P
Adds or removes the 1K ohm pull-down resistor in the
RS-422/RS-485 receiver circuit (Receive data only).
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).
485 receiver circuit (Receive data only).
T
Adds or removes the 120 ohm termination.
L
Connects the TX- to RX- for RS-485 two wire operation.
L
Connects the TX+ to RX+ for RS-485 two wire operation.
P
P
T
L
L
P
T
L
L
Figure 11 - Headers J1E - J4E, Line Termination