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Issue #211 February 2008
RFID Payment Terminal
by Carlos Cossio
Start | System Overview | Energy Transmission | 100% Amplitude Modulation | Load Modulation | MIFARE Card | MIFARE and ISO 14443 | Pay as You Go | Hardware Design | Antenna Design Rules | Antenna Size | Directly Matched Antenna | Firmware Design | Catch the Wave! | Sources & PDF
PAY AS YOU GO
Once the RFID payment terminal is powered up, a Welcome message is displayed on the LCD for several seconds. Following this, the display shows the current date and time and prompts you to enter the required amount using the keypad (see Figure 5).
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| Figure 5—Here is a flowchart of the main menu. Different options are available when a MIFARE card is in the vicinity of the RFID payment terminal. |
The function keys on the keypad are available for maintenance purposes, such as powering the device on and off, setting the date and time, updating the system password, or sending the activity log to a host PC through the serial channel. As soon as you enter a valid amount, the RFID payment terminal starts the transaction process by turning on the RF field and waiting for a contactless MIFARE card in the terminal range, which is about 10 cm. When a valid card is shown, and after the anti-collision procedure and mutual authentication are successfully resolved, the RFID payment terminal asks the contactless MIFARE card for the current balance. If the balance is greater than the requested amount, the transaction can proceed, updating the new balance on the contactless MIFARE card and saving a log record with a time and date stamp in the payment terminal’s flash memory. Otherwise, the payment terminal informs you that the balance is too small and stops the transaction.
If the transaction succeeds, the RFID payment terminal sounds one beep and displays a Thank You message. In the case of a failed transaction, the RFID payment terminal sounds a beep twice. In both cases, at the end of the transaction, the RF field is turned off to save power. When the RFID payment terminal is in an idle state, it is possible to configure some parameters and perform some housekeeping tasks, such as getting the activity log to a host computer and so on.
After pressing the B function key, the LCD shows a message requesting that you enter the new time. The time should be entered in 24-hour format. The system checks that the new time is meaningful; otherwise, it requests the time again. After the time is accepted by the system, the payment terminal requests the desired date, which is entered using the format: DDMMYYYY. Once again, the system ensures that the new date is meaningful to avoid any misconfiguration. At last, the system comes back to the main screen showing the prompt and the updated date and time.
Pressing the C key enables the supervisor password to be changed once the old one has been successfully verified. Pressing the D function key enables the activity log stored in the flash memory of the payment terminal to be sent to a host PC through the serial interface. HyperTerminal could be used to retrieve the log file and should be configured at 115,200 bps, 8 bits of data, 1 stop bit, and no parity bits. Each record of the log file contains the transaction amount, the date, the time, and the card’s serial number.
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