AT88SC0104CA_11 ATMEL [ATMEL Corporation], AT88SC0104CA_11 Datasheet - Page 29

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

8.3.2.2 Random Read: $B1
8.4
The random read command provides the host ability to sequentially clock data from the device starting from a specified
address. The host needs to issue a “dummy” write operation in order to specify the start address for the random read. The
host does this by clocking in the four bytes of the write command and then follows them with a start condition instead of a data
byte. At this point, the device’s internal logic is pointing to the address from the aborted write operation. The host may then
issue the random read command byte ($B1) to which the device will respond with the EEPROM byte at the current address
location and then increment the internal address by one. The device will continue to sequentially send out bytes as long as the
host keeps acknowledging each byte with an ACK. Address “roll over” is from the last byte of the current zone to the first byte
of that zone. The host terminates random read by issuing a NACK signal instead of an ACK.
Figure 8-4. Random Read Command
CryptoMemory will NACK the N parameter of the dummy write operation if the write were issued to an illegal write location.
The NACK response, however, does not affect the loading of the read address. The random read command works for both
configuration and user memory. It is important to implement the CryptoMemory read commands as specified; otherwise
CryptoMemory responses will cause contention on the bus with a host using standard TWI protocol.
Acknowledge Polling
A stop condition ends each command. Certain commands require an acknowledge polling sequence. Acknowledge polling
consists of sending a start condition followed by the command byte and determining if the device responds 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 completed but gives no indication of the success or failure of the
command.
R
S
T
A
T
•
•
•
•
Command
xxxx xxx0
WRITE
Read Commands: No ACK polling required
Write Commands: ACK polling required except encrypted write commands. Any command may be used
Set commands:
Verify commands: ACK polling required with B2 or B6 commands only
C
A
K
0000 0000
Address 1
No ACK polling required
A
C
K
0a6--- ---a0
Address 2
Atmel AT88SC0104CA/0204CA/0404CA/0808CA [Datasheet]
A
C
K
n7--- ---n0
N
N
A
C
K
A
C
K
S
T
A
R
T
Random Read
Command
xxxx 0001
Data
A
C
K
d7--- ---d0
Data
A
C
K
8664E−CRYPTO−12/11
Data x N
d7--- ---d0
N
A
C
K
O
S
P
T
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