SeaI/O Hardware Overview
SeaI/O Base and Expansion Modules
In general, SeaI/O data acquisition modules provide powerful digital, analog, and serial expansion to any host
computer. Multiple modules can be daisy chained using convenient pass-through connectors to create a
versatile distributed control and monitoring network. For ease of installation, multiple modules can be combined
in a local stack or separated up to 4000 feet using the RS-485 expansion interface.
The first SeaI/O module connected to the host computer is considered the Base module and connects to the
host via one of the following interfaces:
•E-Series –Ethernet Modbus TCP
•U-Series –USB Modbus RTU
•M-Series –RS-485 Modbus RTU
•S-Series –RS-232 Modbus RTU
SeaI/O USB serial expansion modules only connect to the host via USB and will operate as a Base module when
connected to digital and analog SeaI/O N-series Expansion Modules.
After the Base unit is installed, up to 246 additional SeaI/O N-Series expansion modules can be added to create
an I/O network. These expansion modules interface via RS-485 and can be located local to the Base SeaI/O
module or remotely located up to 4000 feet away. Local installations (<10’ of cabling) should use the 5” CAT5
RS-485 pass-through cable (Item# CA239) included with each N-series module to connect together two or more
modules. Remote expansion modules (>10’ of cabling) should use twisted pair wiring connected via the
removable screw terminal connectors.
For local installations, power to the expansion modules is supplied from the base module via the pass-through
connectors. For remote devices, separate power is required at each expansion module. Refer to the Power
Options chapter of this manual for more information on SeaI/O power requirements and power supply sizing.
Communicating Via Modbus Commands
Sealevel SeaI/O modules are designed to integrate seamlessly into existing Modbus networks. The supported
command set will vary depending on the SeaI/O model used. While SeaI/O USB serial expansion modules do
not require any Modbus commands to operate, they do pass through all Modbus RTU commands to other
connected SeaI/O modules and Modbus compliant devices.
The SeaI/O Modules manual covers digital and analog I/O modules and details the supported Modbus command
set. The official Modbus specification can be found at www.modbus.org.