The PCI-COM2S is a dual-port, asynchronous serial communications card designed for use in PCI-Bus computers. The board is 165mm long and may be installed in any 3.3V or 5V PCI or PCI-X slot. Each independent port supports RS-232, RS-422 and RS-485 transmission and has the capability to add bias voltage. (RS-485 communication requires that one transmitter in the network must supply a bias voltage to ensure a known "zero" state when all transmitters are OFF). Also, receiver inputs at each end of the network should be terminated to eliminate ringing. The PCI-COM2S supports these options by means of jumpers on the card. Type 16550 UARTs are used as the asynchronous communication elements. These include a 16-byte transmit/receive FIFO buffer to protect against lost data in multitasking systems while maintaining 100 percent compatibility with the original IBM serial port. A crystal oscillator is located on the card and permits precise baud rate capability up to 115,200. Higher baud rates, up to 460,800 baud, are achieved by changing a jumper on the card. The driver/receivers used, type 75ALS180, are capable of driving extremely long communication lines at high baud rates. They can drive up to ±60 mA on balanced lines and receive inputs as low as 200 mV differential signal superimposed on common mode noise of +12V to -7V. In case of communication conflict, the driver/receivers feature thermal shutdown.