PCI one chip solution( SystemBase SB16C1052PCIe)

It's real COM Port in your computer, not USB to COM port
  high compatible with serial type device.

 Mini PCIe 2 Serial  RS422/RS485 in  Windows XP Device Manager

* Standard PCI-e Local Bus Specification Rev 1.0a/1.1 compliant 
* Built-in two improved  16C1050 UART with 256-byte Deep FIFO
* Software/Hardware Flow Control & Xoff Re-Transmit Function
* Easy Plug and Play Installation
 
System Requirements:

 * Windows 98/2000, XP, Server 2003 ,Vista ,Win7 and Linux 2.4 & 2.6

 * Mini PCIe slot

Accessories:

1 x Manual, 1 x Driver CD, 2 x 9pin serial cable