AN2284 datasheet(24/40 Pages) STMICROELECTRONICS

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7 ISO 7816-3 - Electronic Signal and Transmission Protocol

AN2284

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Fixed and variable length files contain records that are identified by a sequence number. In a

fixed-length record file, all the records contain the same number of bytes. In contrast, a

variable-length record file contains records that may vary in length. As a result, variable-length

record files have a higher overhead in read/write access times as well as a higher

administrative overhead required by the file system.

A cyclic file allows applications to access records in a consistent and transparent manner. It can

be thought of as a ring of files. Write operations are performed on the next physical record in

the ring.

7.2.3

The ISO 7816-4 Functions

The few functions that are defined in ISO 7816-4 for selecting, reading and writing to files will

be briefly discussed below.

Select File:

This command establishes a logical pointer to a particular file in the smart card's file system.

This pointer is required for any file manipulation operation. Access to the smart card's file

system is not multithreaded, however it is possible to have several file pointers defined at any

point in time. This is accomplished by the Manage Channel command, which establishes

multiple logical channels between the reader side application and the card. This allows different

files on the card to be in various states of access by the reader application at the same time.

The identification of the file can be provided in the following ways:

●

file identifier (2-byte value)

●

DF name (string of bytes)

●

path (concatenation of file identifiers)

●

short ID

Note that not all smart cards support all four naming mechanisms.

Read Binary:

This command is used by the application on the reader side to retrieve a part of an EF on the

card. However, the EF must be a transparent file (not record-oriented). If the Read Binary

command is attempted on a record-oriented EF, the command will abort with an error indicator

being returned from the card.

The Read Binary command takes two parameters: an offset pointer from the start of the file to

the initial byte to be read, and the number of bytes to be read and returned to the reader.

Write Binary:

This command is used to insert data into a transparent EF on the card. This command can be

used to set a series of bytes in the EF (i.e. set selected bits within a specified byte to a value of

1), clear a series of bytes or perform a write of a series of bytes in the EF.

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