at88sc0104c ATMEL Corporation, at88sc0104c Datasheet - Page 30

• Manufacturer Part Number: at88sc0104c
• Description: Cryptomemory Specification For Standard Mode Of Operation
• Manufacturer: ATMEL Corporation

7.4
26
Acknowledge Polling
AT88SC0104/0204/0404/0808/1616/3216/6416/12816/25616C
Figure 7-1.
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.
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.
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.
R
S
T
A
T
S
A
R
T
T
Command
Address
xxxx xxx0
Device
xxxx 0x10
TWI Write Command:
CryptoMemory Read Command
A
C
K
A
C
K
Address 1
Address 1
xxxx xxxx
xxxx xxxx
Word
A
C
K
C
A
K
Address 2
Address 2
xxxx xxxx
xxxx xxxx
Word
C
A
K
C
A
K
xxxx xxxx
xxxx xxxx
N
N
A
C
K
A
C
K
d7--- ---d0
d7--- ---d0
Data
Data
A
C
K
C
A
K
Data X N
Data x N
d7--- ---d0
d7--- ---d0
5210A–SMIC–04/07
C
A
K
N
A
C
K
O
S
P
T
O
S
T
P