AT88SC0104C datasheet(29/58 Pages) ATMEL

29 / 58 page

5210B–SMIC–11/08

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

Figure 7-1.

TWI Write Command:

All CryptoMemory commands will have a zero for the LSB of the first byte. All CryptoMemory

commands will have 4 bytes used for defining the command and addressing the memory. All

but the CryptoMemory read commands will send an additional 0 to 128 bytes of data following

the 4 command bytes. These commands comply with the format of a TWI write command.

The CryptoMemory read commands (Read User Zone, System Read) do not comply with the

format of a TWI write or read command. The CryptoMemory read command looks like a TWI

write command (LSB of the first byte = 0) but after the 4th byte of the command the CryptoMem-

ory device will begin to send data back on the bus. The number of bytes sent by CryptoMemory

will be equal to the value of N.

Figure 7-2.

CryptoMemory Read Command

The response of CryptoMemory will cause contention with the host on a standard TWI bus. Typ-

ically CryptoMemory cannot be used on a standard TWI bus but requires a modified TWI

protocol to account for the unique read command format.

7.4

Acknowledge Polling

Each command is ended with a stop condition. Certain commands are required to be followed

by an acknowledge polling sequence. Acknowledge polling consists of sending a start condition

followed by the command byte and determining if the device responded with an ACK. If the

device is not ready for the command it will not acknowledge and the sequence must be repeated

(start condition, command byte, check for ACK). The ACK indicates the operation has com-

pleted but gives no indication of the success or failure of the command.

• Read Commands: No ACK polling required.

Device

Address

Word

Address 1

Word

Address 2N

Data

Data X N

xxxx xxx0

xxxx xxxx

d7--- ---d0

Command

Address 1

Address 2

Data

Data x N

xxxx 0x10

xxxx xxxx

d7--- ---d0

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