AT88SC0104CA_11 ATMEL [ATMEL Corporation], AT88SC0104CA_11 Datasheet - Page 28

• Manufacturer Part Number: AT88SC0104CA_11
• Description: Atmel CryptoMemory Specification Datasheet
• Manufacturer: ATMEL [ATMEL Corporation]

8.3
8.3.1
8.3.2
8.3.2.1 Normal Read: $B2 or $B6 (Read User Zone or System Read)
Command Format
Most CryptoMemory commands have the same format as a two wire interface (TWI) write command characterized by a zero in
the LSB of the first byte (device address). The only exception is the random read command that has a one in the LSB of the
device address byte.
Write Command Format
The host generates all command and data bytes within a write transaction and sends these to the device. The device
acknowledges each byte.
Figure 8-2. CryptoMemory Write Command
The number of bytes CryptoMemory can write within each call of a write command is constrained by the physical page size of
the EEPROM memory. The maximum number of bytes to write for each call to the write command is $10. All CryptoMemory
write commands comply with the format for the TWI write command.
Read Command Format
The CryptoMemory read commands (read user zone, system read and random read) do not comply with the format of the TWI
read command. The CryptoMemory read user zone and system read commands closely resemble the TWI write command
format by having a zero in the LSB in the device address byte. The random read command closely resembles the format for
the TWI read command but requires additional steps to specify the read address.
The CryptoMemory normal read command looks like a TWI write command (LSB of the fist byte = 0) but after the fourth byte of
the command the CryptoMemory 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 8-3. CryptoMemory Normal Read Command
The response of CryptoMemory will cause contention with the host on a standard TWI bus. Typically CryptoMemory cannot be
used on a standard TWI bus but requires a modified TWI protocol to account for the unique read command format.
S
T
A
R
T
S
T
A
R
T
Command
Command
xxxx xxx0
xxxx xxx0
WRITE
READ
C
A
C
K
A
K
Address 1
Address 1
0000 0000
0000 0000
A
C
K
C
A
K
Address 2
Address 2
0a6-- ---a0
0a6-- ---a0
A
C
K
Atmel AT88SC0104CA/0204CA/0404CA/0808CA [Datasheet]
A
C
K
n7--- ---n0
n7--- ---n0
N
N
C
A
K
C
A
K
d7--- ---d0
d7--- ---d0
Data
Data
A
C
K
A
C
K
Data x N
d7--- ---d0
Data x N
d7--- ---d0
N
A
C
K
C
A
K
O
S
T
P
S
O
P
T
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