AT88SC0104CA-SH Datasheet, PDF (44/66 Pages) ATMEL Corporation – Atmel CryptoMemory Specification Datasheet

10. Asynchronous T=0 Protocol
10.1
Character Format
The CryptoMemory complies with the asynchronous T=0 protocol defined in ISO 7816-3. The character format is shown in the
following figure. Note that the byte is transmitted with the least significant bit first.
Figure 10-1. Character Format
Z Start bit
8 data bits
Parity bit Next Start bit
I/O
d0 d1 d2 d3 d4 d5 d 6 d 7 p Guard Time
A
0 t1
(n ± 0,2) etu
tn
t 10
Even parity is used: the parity bit is such that the overall sum of bits in the data byte and the parity 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.
10.2
Command format
The command sequence is as follows:
1. In compliance with ISO 7816-3, the host must send the header consisting of five characters: 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
2. 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
3. Data transfer (P3 bytes)
4. A final SW1-SW2 sequence gives the status of the device after completion of the command. 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)
Atmel AT88SC0104CA/0204CA/0404CA/0808CA [Datasheet]
44
8664E−CRYPTO−12/11