AN2646 datasheet(20/43 Pages) STMICROELECTRONICS

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ISO 7816-4 – smartcard commands

AN2646 - Application note

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The ACK byte is a repeat of the INS byte from the command TPDU. If the response does not

reach the reader within a specified time, the reader may initiate an RST sequence to restart

the protocol between the reader and the card. This can be prevented if the reader receives

at least one NULL byte from the card. SW1 informs the reader of the result of the requested

instruction. The values allowed for SW1 are defined as part of the application protocol.

Some instructions require the card to send data to the reader. In this case SW2 is returned

to the reader, triggering the reader to execute a GetResponse command. The card will then

return the data bytes generated by the execution of the previous command.

5.2

Application-level protocols

The ISO 7816-4 standard addresses two areas of functionality for application software:

●

File system: a set of functions is provided in the form of an API. By using this API

application software on the reader side can access files in the file system.

●

Security functions: these can be used to limit access to application software or to files

on the card.

The T0 protocol is used to support application-level protocols between the smartcard

application and the reader application. These application protocols exchange data

structures called application protocol data units (APDUs). The following diagram illustrates

this architecture:

Figure 6.

Application communication architecture

The APDU structure defined by ISO 7816-4 is very similar to the TPDU structure used in the

T0 protocol. In fact, when an APDU is transported by the T0 protocol, the elements of the

APDU directly overlay the elements of the TPDU.

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