AN2385 Freescale Semiconductor / Motorola, AN2385 Datasheet - Page 2

• Manufacturer Part Number: AN2385
• Description: GPRS Wireless Internet Connectivity Using DragonBall and Palm OS Based PDAs Application Note
• Manufacturer: Freescale Semiconductor / Motorola

GSM-GPRS Application
Both dial-up and GPRS connections have hardware and software components associated with them. The
Timeport™ 280 mobile phone has a built-in modem, and this modem is the major hardware component
connecting the client (in this case the PDA) with the Internet. The information (data stream) as received by
the modem cannot be used directly by the PDA. Therefore, software implementing the point-to-point
protocol (PPP) suite and a world-wide Web browser are required for both types of connection. PPP is a
standard part of the Palm OS network stack and is available on all Web-enabled Palm OS PDAs. The
browser can be installed as a separate application on the PDA.
This reference application uses the Eudora Web browser. The Eudora Internet Suite 2.1 for the Palm
Computing Platform can be downloaded at no cost from the following location:
http://www.eudora.com/internetsuite/download/
The network setup of dial-up and GPRS connections for mobile Internet access on Palm OS look the same.
The difference lies in the protocol implementation and the inner working of the two setups, which remain
hidden to the end user. The difference perceived by the end user lies in the steps performed to establish the
connection.
In the case of a dial-up connection, the user might need to create a specific dial-up profile consisting of
information like user name, password, ISP’s dial-up number, and so on. The PDA’s built-in networking
software then handles dialing the ISP’s phone number, supplying the user name and password, and
performing the PPP negotiations when prompted by the user. Once the connection is established, the user
is informed by a message on the screen, signaling that the Web browser can be started.
The steps to establish a GPRS-based connection are slightly different. Having a GPRS-enabled phone does
not ensure GPRS-based Internet access. The phone service provider must support the GPRS service and
the user must subscribe to this service. Assuming that these conditions are met, establishing a connection
involves sending a number of commands known as “AT commands” to the modem of the GPRS-enabled
mobile phone. Using the PDA as it is, the user must create a lengthy setup script which must be run to
establish the connection. Creation of this script (although a one-time job) is time consuming.
The GSM-GPRS application described in this paper simplifies the connection process and runs the Web
browser automatically for GPRS-based Internet access. With this application, mobile Internet access is just
a click away. Also, this application provides a dial key interface to initiate and receive mobile voice calls.
This key implementation can be modified to create more elaborate phone applications.
3 GSM-GPRS Application
The GSM-GPRS application’s main objective is to establish an Internet connection using the mobile
phone’s internal modem and then launch the Eudora Web browser programatically. In addition, the
application can initiate and receive GSM voice calls.
For all communication with the mobile phone, the application uses the PDA’s RS-232 serial
communication port. Software flow control is used, and therefore RTS and CTS signal lines are used in
addition to Tx, Rx, and GND lines for interface with the mobile phone. The speed of serial communication
between the PDA and the mobile phone is set at 57.6 kbps.
3.1 Graphical User Interface (GUI)
The user interacts with the GUI for two purposes:
The application does not provide features such as phone book, record of incoming and outgoing calls, and
so on, on the PDA. However, the application can be modified by a programmer for such purposes.
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To launch the GPRS-based Internet access
To place and receive voice calls
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