Impulse 3189 User Manual
Page 9
Card Setup
Sealevel Systems ULTRA-SIO Page
6
RTS
Auto
E8 & E10
E3 & E9
Figure 8 - RS-485 ‘Auto’ Enabled, with ‘Echo’
RTS
Auto
E8 & E10
E3 & E9
Figure 9 - RS-485 ‘RTS’ Enabled, with ‘No Echo’
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 E1 and E4 allow the user to customize this interface to their
specific requirements. Each jumper position corresponds to a specific portion of the interface. If multiple
Ultra-SIO
adapters are configured in a 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
L
Connects the TX+ to RX+ for RS-485 two wire operation.
T
Adds or removes the 120 ohm termination.
L
Connects the TX- to RX- for RS-485 two wire operation.
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
T
L
P
P
Figure 10 - Headers E1 and E4, Line Termination