Hardware manual

this to /etc/udev/udev.rules
BUS=="pci" KERNEL=="ttyS3", NAME="ttyS14"
On-board serial ports on motherboards which have both PCI and ISA slots are likely to still be ISA ports.
Even for all-PCI-slot motherboards, the serial ports are often not PCI. Instead, they are either ISA, on an
internal ISA bus or on a LPC bus which is intended for slow legacy I/O devices: serial/parallel ports and
floppy drives.
10.3 Serial Port Device Names & Numbers
Devices in Linux have major and minor numbers. The serial port ttySx (x=0,1,2, etc.) is major number 4. You
can see this (and the minor numbers too) by typing: "ls -l ttyS*" in the /dev directory. To find the device
names for various devices, see the "devices" file in the kernel documentation.
There formerly was a "cua" name for each serial port and it behaved just a little differently. For example,
ttyS2 would correspond to cua2. It was mainly used for modems. The cua major number was 5 and minor
numbers started at 64. You may still have the cua devices in your /dev directory but they are now deprecated.
For details see Modem-HOWTO, section: cua Device Obsolete.
For creating the old devices in the device directory see:
Creating Devices In the /dev directory
10.4 More on Serial Port Names
Dos/Windows use the COM name while the messages from the serial driver use ttyS00, ttyS01, etc. Older
serial drivers (2001 ?) used just tty00, tty01, etc.
The tables below shows some examples of serial device names. The IO addresses are the default addresses for
the old ISA bus (not for the newer PCI and USB buses).
dos common IO USB-BUS ( ACM => acm modem )
name name major minor address || common name common name
COM1 /dev/ttyS0 4, 64; 3F8 || /dev/ttyUSB0 | /dev/ttyACM0
COM2 /dev/ttyS1 4, 65; 2F8 || /dev/ttyUSB1 | /dev/ttyACM1
COM3 /dev/ttyS2 4, 66; 3E8 || /dev/ttyUSB2 | /dev/ttyACM2
COM4 /dev/ttyS3 4, 67; 2E8 || /dev/ttyUSB3 | /dev/ttyACM3
- /dev/ttyS4 4, 68; various
10.5 USB (Universal Serial Bus) Serial Ports
For more info see the usb subdirectory in the kernel documentation directory for files: usb-serial, acm, etc.
10.6 Link ttySN to /dev/modem
On some installations, two extra devices will be created, /dev/modem for your modem and /dev/mouse
for a mouse. Both of these are symbolic links to the appropriate device in /dev.
Historical note: Formerly (in the 1990s) the use of /dev/modem (as a link to the modem's serial port) was
discouraged since lock files might not realize that it was really say /dev/ttyS2. The newer lock file system
Serial HOWTO
10.2 The PCI Bus 38