To configure your Sealevel SeaPORT Plus 2 2203 USB to 2-Port Serial Interface Adapter, follow these steps. First, you'll need to open the device by removing the four screws from the bottom. This gives you access to the internal components. The device uses DIP switches and DIP shunts to configure each port for RS-232, RS-422, or RS-485 interfaces. Here's a breakdown of the switch functions: L 485 option (Off for 422): OFF has no effect, while ON connects TX+ to RX+ for two-wire operation. Another L 485 option (Off for 422): OFF has no effect, and ON connects TX- to RX- for two-wire operation. PU 485 option (Off for 422): OFF has no effect, and ON adds a 1 K ohm pull-up resistor to RX+. PD 485 option (Off for 422): OFF has no effect, while ON adds a 1 K ohm pull-down resistor to RX-. T 422 and 485 option: OFF has no effect, while ON adds a 120-ohm termination resistor between RX+ and RX-. For example, in 485 mode, OFF is for 422 mode, where transmitter lines TX+ and TX- are always active. ON sets the device to 485 mode, switching the transmitter lines to high impedance when not transmitting data. The electrical interface selection is made on a per-port basis using the shunts. For RS-232, set the shunt to the 232 positions and the switches will have no effect. For example, for Port 2 to operate in RS-485 two-wire communication without echo, set the shunt to the 422/485 position, and set switches 485 2, NE 2, and Port 2 L, L, T, PU, and PD all to the ON position. Finally, when reassembling the device, ensure the top and bottom are aligned correctly, as they only fit together in one orientation.
