PC Serial Ports
2.For best performance with the PassageWay Service Provider, choose a card that has hardware support for high-speed communications.
The PassageWay Service Provider operates at a relatively high data rate (9600 baud), and it relies on Windows to manage the flow of data through your PC's serial port. Depending upon your configuration, Windows may have problems maintaining high data rates through traditional serial ports. In these situations, a serial port designed for high-speed communications can eliminate such problems while providing a reduced load on the microprocessor (thus increasing the performance of Windows during data transfers relative to standard serial ports). In most cases, the price differential for such a card is quite modest and a worthwhile investment.
Many serial port cards on the market (and most built-in serial ports) use either the 8250 or 16450 Universal Asynchronous Receiver Transmitter (UART) as their key component. Although these UARTs can operate at high speeds, they do not assist the PC's microprocessor in dealing with high-speed data transfer. Under Windows, in particular, data can be lost at high baud rates using these UARTs. If this data loss occurs, the PassageWay Service Provider cannot function properly.
Whenever possible, select a serial port card that uses the 16550 UART. This industry-standard UART is an improved version of the 16450 with hardware support to help offload the microprocessor during high-speed data transfers. Windows 3.1 has built-in support for the 16550, so no special software configuration is required to obtain the benefits of the 16550's enhanced capabilities. In addition, any high-speed peripheral can benefit from the 16550 (for example, a 9.6-Kbps or 14.4-Kbps data and/or fax modem), not only the PassageWay Service Provider.
In general, since there is no way of knowing ahead of time if your particular PC configuration requires an enhanced serial port for the PassageWay Service Provider, Lucent strongly recommends that you purchase a card based on the 16550 UART to insure trouble-free operation with the PassageWay Service Provider.
