Modem Driver

The Modem Driver controls an attached modem, dials an outgoing target number, and handles incoming calls. The Modem Driver is used when the PPP or SLIP serial network interface is enabled. You must use a Null_Modem driver for the zero-modem link if you use a serial cable to connect the embedded device directly to a computer.

The required functions for the driver are:

• modem_init() - initialize the modem
• modem_dial() - dial a target number
• modem_listen() - initialize the modem to accept incoming calls
• modem_hangup() - stop the connection
• modem_online() - check if the modem is online
• modem_process() - process a character received from the modem in command mode
• modem_run() - the main thread for the modem driver.

RL-TCPnet includes two modem device drivers which are located in the \Keil\ARM\RL\TCPnet\User directory:

• Null_Modem.c is a zero-modem link driver used when a computer is connected directly to the target hardware. The computer simulates a real modem. The Null_Modem driver responds to modem commands sent from a computer in the same way as it responds to a real modem. It also works with the direct cable connection link supported by MS Windows.
• Std_Modem.c is a standard modem driver. This driver works with most of the currently available modems. Use the standard modem driver when a real modem is used to access the embedded device over a public telephone network.

You can copy these files into your project folder or use them as a template to write your own modem driver.

• You need to include only one modem driver into your project for the PPP or SLIP interface. For a zero-modem link, this is not required because the default Null_Modem driver is already in the RL-TCPnet library.
• If you want to customize the Null_Modem.c modem driver, copy it from the \Keil\ARM\RL\TCPnet\User directory and add it to your project. Then customize it as needed.