All APDUs are received by the Java Card RE and preprocessed. All commands, except for the MANAGE CHANNEL command result in an instance of the APDU class containing the command being passed to the process(APDU) method of the currently selected applet.

Note - A SELECT FILE APDU command might cause a change in the currently selected applet prior to the call to the process method. The actual change occurs before the call to the select method.

On normal return, the Java Card RE automatically appends 0x9000 as the completion response status word to any data already sent by the applet.

At any time during process, the applet may throw an ISOException with an appropriate status word, in which case the Java Card RE catches the exception and returns the status word to the CAD.

If any other exception is thrown during process, the Java Card RE catches the exception and returns the status word ISO7816.SW_UNKNOWN to the CAD.