The BLS 4221S is a high-performance RS422/485 card with a 16C550-style UART that features 16-byte transmit and receive buffers to help guard against loss of data in your busy system. The card may be addressed as COM1: to COM4: or any other I/O address you choose from 000 up to 3F8 hex. The backplate has one standard DB-9 male (9-pin) connector.
All ports are capable of operating at speeds up to 460 kbaud simultaneously, making this card ideal for high-speed applications such as ISDN modems.
Interrupt Sharing: The Key to Adding Many Serial Ports
The powerful interrupt feature allows multiple ports on a single card to use the same interrupt. Any of eleven interrupt choices are available for each port. The card is jumper-selectable for compatibility with protocols used by Digi®. This functionality provides drop-in replacement capability at reduced cost. Because each port's address may be defined individually, you don't have to worry about address conflicts the way you would with cards that use 32- and 64-byte blocks for addressing. Our serial cards are compatible with all application software that communicates with a standard serial port using an 8250 or 16C450 UART (the UARTs which virtually all PC's use for serial ports). This includes compatibility with DOS, Windows 3.x/95/98/NT/ME/2000/XP, OS/2, UNIX, and XENIX. RS-232 cards support the standard RS-232 interface and all the above mentioned features; they're DTE/DCE selectable so no special cables are required. Each port supports all handshake and modem control lines, including: TXD, RXD, RTS, CTS, DSR, DCD, DTR, and RI.
Drivers are automatically and instantly disabled (and receivers enabled) after transmission of the stop bit. Drivers and receivers may also be controlled with data bits 0 and 1 by writing to the base address+7 for the port (MetraByte COM-485 protocol compatible). RTS and CTS flow control is supported as well. Convenient on-board jumpers allow for 220-ohm termination as needed for each driver and receiver.