### About RealPort Devices

When installed, the Linux RealPort driver creates three different devices for each physical port of each Digi device: a standard TTY device, a callout device, and a transparent print device.

#### Device Naming Convention

The devices are named according to the following convention:

> [prefix][ID][port]

These elements are defined as follows:

Element | Description
prefix | Standard TTY devices have the prefix “tty”, callout devices have the prefix “cu”, and transparent print devices have the prefix “pr”.
ID | The RealPort ID for the Digi device associated with this port. A RealPort ID consists of one or two alphanumeric characters. An underscore character may be used for any of the two ID characters.
port | The port number must consist of two digits. The ports are numbered beginning with 00.

The following are examples of the devices which would be created for the first port of a Digi device with the RealPort ID “aa”.

Device Type | Full Path Name
--- | ---
Standard TTY Device | /dev/ttyaa00
Callout Device | /dev/cuaa00
Transparent Print Device | /dev/praa00

#### Standard TTY Devices

The behavior of the standard tty devices is that of a modem controlled port. They require the Data Carrier Detect (DCD) signal to be high before they will operate. When used on a dial-in modem, the ports will wait for DCD before sending out the login prompt.

When these devices are used with a terminal or other locally connected device, it is usually the practice to wire the DCD signal to the remote equipment's Request To Send (RTS) line. When a terminal is then used for log-in, the system will generate a prompt when the terminal is powered-on (RTS, and thus DCD is asserted), and will kill the user session if the terminal is powered-off (lowering the signals).

#### Callout Devices

These devices will be obsoleted in a future version of Linux, so should generally be avoided. Data Carrier Detect (DCD) need not be present to open the device.

Once a connection is established and DCD becomes active, these devices behave in the same way as the standard tty devices. Subsequent loss of the DCD signal will cause active processes on the port to be killed.

#### Transparent Print Devices

The transparent print device can be used with auxiliary printer ports on terminals. Output to the “pr” device goes out the auxiliary port of a terminal while you continue to use the terminal normally.

Important: At the time this document was created, the RealPort software did not support transparent printing, despite the fact that transparent print devices are created when the driver is installed. To determine if transparent printing is supported by a subsequent version of the Linux RealPort driver, check the release notes for that driver.