Installation – Impulse SIO-104+2 (3502) User Manual
Page 7
Card Setup
Sealevel Systems SIO-104+2 Page
5
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.