AN2646 datasheet(16/43 Pages) STMICROELECTRONICS

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ISO 7816-3 – electronic signal and transmission protocol

AN2646 - Application note

16/43

4.3

Answer to reset (ATR)

Once an RST signal is sent from the reader to the card, the card must respond with the first

character of the ATR within 40 000 CLK cycles. The card might not respond with an ATR for

a number of reasons, the most prevalent being that the card is inserted incorrectly into the

reader (probably upside down). In some instances, the card may not be functioning because

it has been damaged or broken. Whatever the case, if the ATR is not returned within the

prescribed time, the reader should begin a sequence to power down the card. During this

sequence, the reader sets the RST, CLK, and I/O lines low and drops voltage on the VCC

line to nominal 0 (that is, less than 0.4 V).

The ATR is a string of characters returned from the card to the reader following the

successful completion of the power-up sequence. As defined in ISO/IEC 7816-3, the ATR

consists of 33 or fewer characters comprising the following elements:

●

TS - a mandatory initial character

●

T0 - a mandatory format character

●

TAi TBi TCi TDi - optional interface characters

●

T1, T2,TK - optional historical characters

●

TCK - a conditional check character

The historical characters can be defined at the discretion of the card manufacturer or the

card issuer. These characters are typically used to convey some type of designation of the

type, model, and use of this specific card. When used in this way, the historical characters

provide a mechanism through which systems can automatically detect the use of an

inserted card (within that system) and can initiate other actions (or software) accordingly.

The check character provides a mechanism through which the integrity of the ATR can be

measured; that is, whether a transmission error has occurred in sending the characters from

the card to the reader.

The structure of the ATR is illustrated in Table 7. As discussed previously, the initial TS

character is used to establish the bit-signaling and bit-ordering conventions between the

reader and the card. The T0 character is used to signal the presence or absence of

subsequent interface characters or historical characters. The interface characters are used

to tailor the characteristics of the I/O channel, including the specific protocol used by the

card and reader during subsequent exchange of commands (from the reader to the card)

and responses (from the card to the reader). The historical characters, if present, are used

to convey card-manufacturer-specific information from the card to the read, and hence to the

application system being served by the reader. There is really no established standard for

the information presented in the historical bits.

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