Impulse 463N - Manual (Page 52)

©Sealevel Systems, Inc.
SL9049 - 11/2010
SeaI/O Manual 52
A “stack” or “chain” of SeaI/O modules, connected via the pass-through connectors or screw
terminals on the left side of the enclosure, communicates via an RS-485 bus, which must be
properly terminated to work correctly. A set of three dipswitches is located on the left side of
enclosure, next to the “ADDR” rotary switch. These switches control line termination and the RS-485
pull-up and pull-down resistors.
The pull-up and pull-down resistors ensure that the input ports are at a known state when not
being driven by the RS-485 line. In most cases, all three of the dipswitches on each SeaI/O module
should be in the down position, except the two end modules. The first and last SeaI/O modules in
the chain should have all three dipswitches in the up (enabled) position.
Make sure that only the first and last SeaI/O modules have line termination enabled (up
position). Improper termination settings can result in invalid data or communication
failures.