May 2006, Issue 190

Mobile Phone Book
M16C/62P-Based Data Backup System
Renesas M16C 2005 Honorable Mention

COMMUNICATION MODEL

There’s a half-duplex communication pathway between the smart card and the host. This means that data can be sent from either the host to the card or from the card to the host, but not at the same time.

Two PCs communicate with each other by exchanging data packets, which are constructed following a protocol such as TCP/IP. Similarly, smart cards speak to other PCs via data packets called application protocol data units (APDUs). An APDU contains either a command or a response message.

The master-slave model applies to smart cards. A smart card always plays the passive slave role. When it receives a command APDU from an external device, it executes the instruction specified in the command and replies to the external device with a response APDU. Command  and response APDUs and are exchanged between a card and an external device.