X76F641 データシートの表示（PDF） - IC MICROSYSTEMS

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X76F641

Secure Serial Flash

IC MICROSYSTEMS 

X76F641

Figure 1. X76F641 Device Operation

LOAD COMMAND BYTE

LOAD 8-BYTE

PASSWORD

VERIFY PASSWORD

ACCEPTANCE BY

USE OF PASSWORD ACK POLLING

Start Condition

All commands are preceded by the start condition,

which is a HIGH to LOW transition of SDA when SCL is

HIGH. The X76F641 continuously monitors the SDA and

SCL lines for the start condition and will not respond to

any command until this condition is met.

A start may be issued to terminate the input of a control

byte or the input data to be written. This will reset the

device and leave it ready to begin a new read or write

command. Because of the push/pull output, a start can-

not be generated while the part is outputting data. Starts are

inhibited while a write is in progress.

LOAD 2 BYTE ADDRESS

READ/WRITE

DATA BYTES

Stop Condition

All communications must be terminated by a stop condi-

tion. The stop condition is a LOW to HIGH transition of

SDA when SCL is HIGH. The stop condition is also used to

reset the device during a command or data input

sequence and will leave the device in the standby power

mode. As with starts, stops are inhibited when outputting

data and while a write is in progress.

Twc OR DATA ACK POLLING

Acknowledge

7025 FM 03

Acknowledge is a software convention used to indicate

Retry Counter

successful data transfer. The transmitting device, either

master or slave, will release the bus after transmitting

The X76F641 contains a retry counter. The retry counter eight bits. During the ninth clock cycle the receiver will

allows 8 accesses with an invalid password before any pull the SDA line LOW to acknowledge that it received the

action is taken. The counter will increment with any com- eight bits of data.

bination of incorrect passwords. If the retry counter over-

flows, all memory areas are cleared and the device is The X76F641 will respond with an acknowledge after

locked by preventing any read or write array password recognition of a start condition and its slave address. If

matches. The passwords are unaffected. If a correct both the device and a write condition have been

password is received prior to retry counter overflow, the selected, the X76F641 will respond with an acknowledge

retry counter is reset and access is granted. In order to after the receipt of each subsequent eight-bit word.

reset the operation of a locked up device, a special reset Reset Device Command

command must be used with a RESET password.

The reset device command is used to clear the retry

Device Protocol

counter and reactivate the device. When the reset device

The X76F641 supports a bidirectional bus oriented proto- command is used prior to the retry counter overflow, the retry

col. The protocol defines any device that sends data onto counter is reset and no arrays or passwords are

the bus as a transmitter and the receiving device as aaffected. If the retry counter has overflowed, all memory

receiver. The device controlling the transfer is a master areas are cleared and all commands are blocked and the

and the device being controlled is the slave. The master willretry counter is disabled. Issuing a valid reset device

always initiate data transfers and provide the clock for

command (with reset password) to the device resets and

both transmit and receive operations. Therefore, the re-enables the retry counter and re-enables the other

X76F641 will be considered a slave in all applications.

commands. Again, the passwords are not affected.

Clock and Data Conventions

Data states on the SDA line can change only during SCL

LOW. SDA changes during SCL HIGH are reserved for

indicating start and stop conditions. Refer to Figure 2 and

Figure 3.

Reset Password Command

A reset password command will clear both arrays and set all

passwords to all zero.

3

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