What are the names of the serial ports?

# 3 What are the names of the serial ports?

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There are the 4 serial devices corresponding to COM1 - COM4:

> `

>     /dev/cua0, /dev/ttyS0 (COM1) address 0x3f8 IRQ 4
>     /dev/cua1, /dev/ttyS1 (COM2) address 0x2f8 IRQ 3
>     /dev/cua2, /dev/ttyS2 (COM3) address 0x3e8 IRQ 4
>     /dev/cua3, /dev/ttyS3 (COM4) address 0x2e8 IRQ 3

> `

The `/dev/ttyS`N devices are for incoming connections and `/dev/cua`N devices for outgoing connections. N is the serial port number. In this document, I refer to COM1 as `ttyS0`, COM2 as `ttyS1`, COM3 as `ttyS2`, and COM4 as `ttyS3`. If I am refering to a specific device in `/dev`, I will always prepend `/dev` to avoid confusing you.

On some installations, two extra devices will be created, `/dev/modem` for your modem and `/dev/mouse` for your mouse. Both of these are symbolic links to the appropriate `/dev/cua`N device which you specified during the installation (unless you have a bus mouse, then `/dev/mouse` will point to the bus mouse device).

There has been some discussion on the merits of `/dev/mouse` and `/dev/modem`. I strongly discourage the use of these links. In particular, if you are planning on using your modem for dialin you will run into problems because the lock files will not work correctly if you use `/dev/modem`. Also, Taylor UUCP does not support symlinks either.

## 3.1 Major and minor device numbers of serial devices in `/dev`

> `

>     /dev/ttyS0 major 4, minor 64    /dev/cua0 major 5, minor 64
>     /dev/ttyS1 major 4, minor 65    /dev/cua1 major 5, minor 65
>     /dev/ttyS2 major 4, minor 66    /dev/cua2 major 5, minor 66
>     /dev/ttyS3 major 4, minor 67    /dev/cua3 major 5, minor 67

> `

Note that all distributions come with these devices already made correctly.

### Creating devices in `/dev`

If you don't have a device, you will have to create it with the `mknod` command.

Example, suppose you needed to create devices for `ttyS0`:

> `

>     linux# mknod -m 666 /dev/cua0 c 5 64
>     linux# mknod -m 666 /dev/ttyS0 c 4 64

> `

You can also get the `MAKEDEV` script, available on the usual FTP sites. This simplifies the making of devices. For example, if you needed to make the devices for `ttyS0` you would type:

> `

>     linux# cd /dev
>     linux# MAKEDEV ttyS0

> `

This handles the devices creation for the incoming and outgoing devices.

### Notes for multiport boards

The devices your multiport board uses depends on what kind of board you have. These are listed in detail in the `rc.serial` which comes with the `setserial` program. You will need to create these devices for sure! Either use the `mknod` command, or get the `MAKEDEV` script. Devices for mulitport boards are made by adding 64 + the port number. So, if you wanted to create devices for `ttyS17`, you would type:

> `

>     linux# mknod -m 666 /dev/cua17 c 5 81
>     linux# mknod -m 666 /dev/ttyS17 c 4 81

> `

Note that ``64 + 17 = 81'' Using the `MAKEDEV` script, you would type:

> `

>     linux# cd /dev
>     linux# /dev/MAKEDEV ttyS17

> `

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