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© Sealevel Systems, Inc. 3502 Manual | SL9116 9/2022
Line Termination (Position 4-9)
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-422/485 input in addition to a 1K-ohm pull-up/pull-down
combination that biases the receiver inputs. Switches SW1B and SW2B allows customization of this
interface to specific requirements. Each jumper position corresponds to a specific portion of the interface.
If multiple
SIO-104+2
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
PD
Adds or removes the 1K ohm pull-down resistor in the RS-422/RS-485 receiver circuit (Receive
data only).
PU
Adds or removes the 1K ohm pull-up resistor in the RS-422/RS-485 receiver circuit (Receive data
only).
BS
Use only for RS-422/485
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.
Typical settings for SW1B and SW2B
Mode
(Switch position)
M0 (2)
M1 (3)
PD (4)
PU (5)
BS (6)
T (7)
L (8)
L (9)
RS232
OFF
OFF
OFF
OFF
OFF
OFF
OFF
OFF
RS422
OFF
ON
ON
ON
ON
ON
OFF
OFF
RS485 with echo
ON
OFF
ON
ON
ON
ON*
OFF
OFF
RS485 no echo
ON
ON
ON
ON
ON
ON*
ON
ON
*
If at end of RS485 bus turn termination ON
If in middle leave OFF
Clock Modes
The
SIO-104+2
employs a 7.3728 MHz clock. This provides for data rates up to 460.8Kbps.
