AT88SC0104C datasheet(37/58 Pages) ATMEL

37 / 58 page

5210B–SMIC–11/08

AT88SC0104/0204/0404/0808/1616/3216/6416/12816/25616C

Asynchronous T=0 Protocol

8.1

Character format

CryptoMemory complies with the asynchronous T=0 protocol defined in ISO 7816-3. The char-

acter format is shown in the following figure: note that the byte is transmitted with the least

significant bit first.

Even parity is used: the parity bit is such that the overall sum of bits in the data byte and the par-

ity bit is an even number. If a transmission error is detected, the receiving device indicates this

by applying a low level on the I/O channel during the guard time. This tells the transmitting

device to retransmit the byte.

8.2

Command format

The command sequence is as follows:

In compliance with ISO 7816-3, the host must send the header consisting of 5 charac-

ters: CLA, INS, P1, P2, P3.

CLA refers to a class of instructions. This byte isn't tested by the device.

INS is the instruction byte.

P1 and P2 are reference bytes, such as a data byte address or password index.

P3 is the number of data bytes transferred during the command. For outgoing

transfers (e.g. read commands), P3 = 0 means that 256 data bytes will be emitted

by the card. For incoming commands, P3 = 0 means that no data bytes will be

transferred.

The device replies with a "procedure byte", normally equal to the INS code received. If

a problem occurred, then the device will respond with a status word pair SW1-SW2,

indicating the end of the command.

Data transfer (P3 bytes).

A final SW1-SW2 sequence gives the status of the device after completion of the com-

mand. A normal completion is indicated by SW1-SW2 = $90-$00.

Note: for all bytes transmitted by the device or by the host, including header, procedure, status

and data bytes, if a parity error is detected, the receiver requests that byte to be sent again (see

character format).

(n ± 0,2) etu

Parity bit

Next Start bit

Start bit

Guard Time

dddddddd

I/O

8 data bits

110

4567

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