SB nº AN-2 : Coding and Usage of TA2 (Clarification)

EMVCo Bulletins Application Notes: Bulletin no. 2, November 2001 Coding and Usage of TA2 Second Edition November 2005 This note applies to EMV ’96 Integrated Circuit Card Specification for Payment Systems Version 3.1.1 and EMV 2000 Integrated Circuit Card Specifications for Payment Systems Version 4.0 Book 1. This note is intended to clarify the coding of TA2, and to identify a potential conflict which incorrect coding may introduce into the ATR. Clarification of coding and usage of TA2 The presence of global interface byte TA2 in the ATR is used to indicate to the terminal that the card wishes to operate in specific mode. If the terminal accepts an ATR containing TA2 (specific mode), the terminal must immediately continue using transmission parameters and protocol type that are either indicated elsewhere in the ATR, or implicitly known to it – b5 in TA2 indicates which to use. Bit b8 in TA2 indicates whether a card is capable of changing its mode of operation – b8 set to 0 indicates that it is capable of changing. This bit should be set according the card’s capabilities, but typically for an EMV card it would be set to 0. In EMV, since PPS is not supported, a specific mode ATR is used by the card to indicate that it wishes to use non-default transmission parameters, such as higher values of D. Since parameters being implicitly known by the terminal would not be a workable solution to achieving international interoperability, the parameters to be used must be indicated elsewhere in the ATR. To achieve this, b5 must be set to 0. The least significant nibble of TA2 indicates the protocol that should be used if the specific mode ATR is accepted. Care should be taken that the protocol indicated in TA2 does not conflict with the protocol indicated in the TDi characters of the ATR. In particular in EMV, the first indicated protocol in the ATR must be used for subsequent transmission, and thus the protocol indicated in TA2 must be the same as the first indicated protocol. Failure to ensure this will lead to an invalid ATR that may be rejected by the terminal. Specification change notice: For clarification, in future revisions of the EMV Specifications it is intended to replace the description of TA2 in Book 1, section 4.3.3.5 with the following:

4.3.3.5 TA2 The presence or absence of TA2 indicates whether the ICC will operate in specific mode or negotiable mode respectively following the answer to reset. When present, TA2 conveys information regarding the specific mode of operation where:

• b8 indicates whether the ICC is capable of changing its mode of operation. It is capable of changing if b8 is set to 0, and unable to change if b8 is set to 1.
• b7-b6 are RFU (set to 00)
• b5 indicates whether the transmission parameters to be used following the answer to reset are defined in the interface characters or are implicitly defined. The transmission parameters are defined by the interface characters if b5 is set to 0, or are implicitly defined if b5 is set to 1
• l.s. nibble b4-b1 indicates the protocol to be used in specific mode. Basic response: The ATR shall not contain TA2; the absence of TA2 indicates the negotiable mode of operation. Terminal behaviour: The terminal shall accept an ATR containing TA2 provided that the following conditions are met:
• the protocol indicated in the l.s. nibble is also the first indicated protocol in the ATR
• b5 = 0
• it is able to support the exact conditions indicated in the applicable interface characters and immediately uses those conditions. Otherwise, the terminal shall reject an ATR containing TA2.