There is currently a proposed revision to the ISO to remove ambiguities and to ensure an effective method of operation for changing the protocol type. An APDU is an Application Protocol Data Unit, a TPDU a Transport Protocol Data Unit. If an APDU command response pair has been defined for T=0 and it has. ISO/IEC specifies the power and signal structures, and information exchange between an integrated circuit card and an interface device such as a.
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Introduction To Smart Cards – Page 3. Technical Adviser to Smart Card News. Return to page 2. After the reset signal is applied by the interface device the IC card responds with an answer to reset. For the active low reset mode the IC should respond between and 40, clock cycles after the rising edge of the reset signal.
The answer to reset is at most 33 characters including the initial character and consists of 5 fields. Each of these fields is sent in order as shown in ido The initial character TS is really a bit synchronisation pattern which may be sent in order to determine the data transmission rate auto baud rate sensing and also to determine the sense of the logic. The format of the TS character is shown in figure This shows the two possibilities of the direct and inverse convention.
In isp inverse convention where the logic level 1 is the space or low state the most significant bit is transmitted first.
With the direct convention where the logic level 1 is the mark or high state then the least significant bit is transmitted first. The format character TO provides information necessary to interpret the remaining answer to reset characters.
For example if the most significant bit b8 is set then TD1 is present in the interface characters field. The least significant 4 bits of the TO formal character give the number binary encoded of bytes in the historical field. The use of 4 bits restricts the maximum size of the historical character field to 15 bytes.
They carry information relating to the available communication protocols as well as the programming voltage and current parameters for the EPROM. There is currently a proposed revision to the ISO to remove ambiguities and to ensure an effective method of operation for changing the protocol type and the protocol parameters.
The proposed revisions to the standard may alter this situation. We will discuss the interface bytes and protocol type selection against these proposed revisions but readers are warned that these recommendations are only provisional.
The interface bytes which are optional are defined in figure TA1 defines the basic characters of the serial transmission, FI is the clock rate conversion factor and DI is the bit rate adjustment factor. The binary encoded fields are compared against tables supplied in the standard to achieve actual values for F and D as defined below. An elementary time unit etu is the nominal bit duration used in the character frame.
Thus as described previously is character frame is equal to 12 etu 1 start etu, 8 data etu, 1 parity etu, 2 guard time etu. The default values for F1 and D1 are 1 which is defined in the tables to give a value for F of and D of 1.
Hence the work and initial etu are the same. At these default values the frequency of the clock should be in the range 1MHz – 5MHz. It should be noted that TB2 is used to define the programming voltage with higher granularity 8 bits instead of 5.
TC1 provides the value of N which defines the extra guard time to be used between successive characters. N can be in the range 0 – etu. TD1 indicates the protocol type TDI as between 0 and 15.
The proposed revision defines a new use for the TA2 interface byte which has a special role in the selection of communication protocols and parameters. We will discuss this further in the communications uso. The historical characters may be used to convey information relating to the life cycle iiso the card. There are clearly other possibilities and the use of these characters is still subject to agreement.
This subject is being considered further as part of the emerging part 4 of the ISO standard. At the current time there are two communication protocols that are in general use. Clearly the IC card and the interface device must operate with a common protocol. The method isi which they achieve a common optimum configuration has been the subject of much discussion over the last few years.
This principle is intended to be achieved by the use of protocol type selection PTS. This is effectively a special command sent from the interface device to 781-3 ICC after the answer to reset. A new concept is proposed which identifies the principle of two modes of operation: An ICC that operates in the specific mode cannot accept a PTS command but may be put into the negotiable mode by a further assertion of the reset command.
Although the ICC indicates to the interface device by means of TA2 its capability to change to the negotiable mode, an existing device in the market place may however be unaware of these changes and therefore will not be prepared to reset the card. The operation of these mode changes are shown in figure The TA2 interface byte which is part of the answer to reset data gives the necessary information to allow the appropriate choice of protocol. The coding of this byte when present is shown in figure In fact the presence or otherwise of this byte is used to determine the mode of operation of the card as follows: It 7186-3 be seen that bit 8 in the TA2 byte is used to 78163- the interface device whether the card can change to the negotiable mode.
The PTS command must be issued immediately after the answer to reset and only applies when the IC card is in the negotiable mode. The interface device may choose to operate by using the first indicated protocol after the answer to reset and by using the default values of F and D. This results in an implicit selection of the protocol and the communication parameters. Should the interface device wish to effect any change to this situation then it must issue the PTS command.
This is shown in figure The response from the ICC follows the same format as the request. The PTS0 format character is encoded as shown in figure These parameters are used for defining the work etu elementary time unit.
When the ICC implements the PTS request message correctly it replies by echoing the same request as the response message. If bit 5 of the PTS1 response character is set to zero then the default values of F and D will be used. Interaction between the interface device and the ICC results in successive commands and responses. For this protocol, data can only flow in one direction for the command response pair.
In isl words, either the command message contains data for the ICC or the command request data from the ICC which is then included in is response. The direction of data flow is implicit on the definition of the command and hence both the interface device and the ICC need to have the necessary a-priori knowledge.
When it is required to transfer data in both directions for a particular command then a “get response” command may be used after the primary command to recover the response data. The command message consists of a 5 character header which the interface device sends to the ICC. The command header consists of the following 5 bytes: When P3 is equal to zero the data from the card will be bytes. When data is to be transferred into the card then a zero data transfer is implied.
Other options allow the interface devices to control the Vpp programming voltage as required. izo
The card may optionally send a NULL procedure byte 60hex iwo allows further time for the processing of the command. In this situation the IFD should await a further procedure byte.
There are two status bytes SW1 and SW2. These bytes are sent from the ICC to the interface device on completion of the command to indicate the current card status. The normal response is: ISO defines 5 such error conditions: In terms of the OSI model this protocol operates at layer 2, the data link layer. In essence this protocol puts an envelope around a block of characters which allows: The choice of communication protocol for the ICC is still a hot topic and one has to consider what advantages can be offered isoo the block protocol and then to examine the price that must be paid.
This limitation was really due to the use of a single byte for defining the length of the data related to the command. For this block protocol a command may be initiated by either the IFD or the ICC albeit within the restrictions of the 7186-3. The block protocol also has a more sophisticated error management system. This allows the use of a block error detection code EDC and the ability to re-transmit blocks that are subject to some error condition. Clearly there is a price to be paid for this higher layer protocol.
This article is continued on page 4.