B&B Electronics 3PCIU4 - Manual (Page 16)

Serial Card Setup
10 Chapter 2 Manual Documentation Number 3PCIoUx-1008
In half-duplex operation, the receiver is disabled during transmit (RX ),
and enabled when not transmitting. In full-duplex operation the receiver is
always enabled (RX ON). Since RS-485 transmitters are tri-stated when not
transmitting, the receive inputs must be biased to ensure the media floats in
the Mark state so that the first Space state is detected correctly at the start of
the next transmission.
These serial cards incorporate the necessary biasing to accommodate up to 32
standard nodes. (Typical input resistance (Rin) for each load is 12kΩ).
Provisions are made for custom biasing and/or termination.
Note: For more information on RS-485 Mode refer to Chapter 6
Operating Mode Selection
The hardware address and IRQ for the serial card is set by the Windows
Operating System using driver information files and the Plug and Play OS.
The Operating Mode is set using DIP switches, Device Manager Driver
Settings and by your cable connections and software. Each port on a MIport
card has an associated DIP switch to set its operating mode. The port number
associated with the DIP switch is clearly silk screened on the printed circuit
board.
Note: Refer to Appendix x for DIP switch locations on various MIport
cards.