USB to Serial

ID #1011

Can I use the USB-COM in other operating systems than Windows?

This depends on the operating system. It is possible to use the USB-COM in Linux since kernel 2.4.x. The drivers are provided by the manufacturer of the central chip in USB-COM. Please check this website for detailed information about support for your OS.


Some special advises:


Are there drivers for Windows NT available?

No, there are no drivers available for Windows NT.

This is because Windows NT is not a USB-capable operating system as standard. There are companies who can provide a USB stack to allow Windows NT to support USB, but FTDI do not support this. 


Are there drivers for MS-DOS available?

No, there are no drivers available for MS-DOS.

Unlike Windows, native MS-DOS has no in-built operating support for USB hardware, so FTDI do not support it.

The possibility of using our USB devices under MS-DOS has been investigated and the answer seems to be that it may work but it depends on several things:

  • Our USB devices will not work on a 'straight' MS-DOS computer as there is no USB stack in MS-DOS and there are no MS-DOS software drivers for the virtual COM port.
  • For the device to function, the Windows VCP drivers must be installed. An MS-DOS application running in a 'DOS-box' under Windows may then be able to access the USB device through the Windows drivers, but it depends upon how the MS-DOS application program was written.
  • In MS-DOS, there are a number of ways the RS-232 serial communication may be set up. The computer BIOS contains a number of INT14 routines to initialise the COM port, set the Baud rate and data format, control handshaking (flow control) and send and receive data. These functions can also be achieved by writing to the hardware (UART registers) directly, by-passing the INT14 routines. If an application is written with all RS-232 communications handled through the BIOS INT14 routines then it may work. However, if the application program is written to bypass the INT14 routines and address the UART hardware directly then it probably will not work.   
  • When a computer is switched on the BIOS routines carry out a Power-On-Self-Test (POST) examining the computer hardware to see what is present and verifying it is functioning correctly. An area of memory, the BIOS Data Segment at segment 0x40, is used to store information about the hardware present. The first four words hold the I/O base addresses of the four serial ports COM1 to COM4. If the port is not present, a zero is entered. Typically, the address for COM1 is 0x03F8 and for COM2 is 0x02F8. During POST the virtual COM port will not exist and so no entry will be made in the BIOS Data Segment table. If an MS-DOS application running in a DOS-box examines the BIOS Data Segment to check for the existence of a serial port then a 'virtual' serial port will not be found.

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Last update: 2009-03-19 17:47
Author: Support
Revision: 1.1

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