National Instruments 4 Ports PCI RS232 adapter 

The National Instruments PCI-8430/4 is a high-performance, 4-port serial interface board for high-speed communication with RS232 devices at rates of up to 1 Mb/s. High-performance RS232 interfaces are also available in two and eight port versions. The NI PCI-8430/4 offers flexible baud rates for data transmissions between 57 b/s and 1 Mb/s to within 1% accuracy for nonstandard baud rates and 0.01% accuracy for standard baud rates. With the high-performance DMA engine, you achieve high throughput with minimal CPU usage. With hyperthreading and multiprocessor support, you can take advantage of the latest PC technology for higher speeds and better efficiency. National Instruments also offers easy-to-use powerful software that significantly reduces your development time for systems that use serial communication with the PCI-8430/4.