Is the 7203e PCIe serial interface dip switch or software configurable to change the RS-485 termination from a 120 Ohm resistor to an AC termination?

Sealevel’s 7203e does have onboard dip switches that would allow you to turn off the 102 Ohm resistor; the 120 Ohm resistor can be changed through dip switches on the board.

Each port on the 7203e has the ability to be used as RS-232, RS-422 or RS-485. This is selectable via two DIP-switches, SW1 & SW2. Please use the following examples to configure your adapter.

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 SW1 and SW2 allow the user to customize this interface to their specific requirements. Each switch position corresponds to a specific portion of the interface. If multiple UltraCOMM+2i.PCIe 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:

For more information about configuration of the 7203e PCI Express serial interface, please see the complete 7203e manual.