X76F128 Datasheet, PDF (8/17 Pages) Xicor Inc. – Secure SerialFlash

X76F128
PASSWORDS
The sequence in Figure 8 shows how to change (pro-
gram) the passwords. The programming of passwords is
done twice prior to the nonvolatile write cycle in order to
verify that the new password is consistent. After the eight
bytes are entered in the second pass, a comparison
takes place. A mismatch will cause the part to reset and
enter into the standby mode.
Data ACK polling can be used to determine if a password
has been loaded correctly, however the data ACK com-
mand must be issued less than 2ms after the stop bit.
After this time, it cannot be determined if the password
has been loaded correctly, without trying the new pass-
word. To determine if the new password has been loaded
correctly the data ACK polling command is issued imme-
diately following the stop bit. If it returns an ACK, then the
two passes of the new password entry do not match. If it
returns a "no ACK" then the passwords match and a high
voltage cycle is in progress. The high voltage cycle is
complete when a subsequent data ACK command
returns an "ACK".
There is no way to read any of the passwords.
Figure 8. Change Passwords
SDA _S
COMMAND
Old
Password
7
Old
Password
0
Wait t_WC
OR
Repeated
ACK Polling
Command
If ACK, then
Password Matches
ACK POLLING
COMMAND
S
Two bytes of “0”
New
Password
7
New
Password
0
New
Password
7
Password
0
Data ACK
Polling
If immediate ACK,
S ^{then New Password error}
If immediate NACK,
followed by ACK after ~5ms
then New Password OK
7052 FM 13
RESPONSE TO RESET
The X76F128 returns a unique 32 bits response to reset
by implementing the following procedures:
• CS goes LOW
• RST goes HIGH
• SCK toggles Low-HIGH-Low
• RST goes LOW
• Each subsequent clock forces next response to
reset bit onto SO pin.
For the X76F128, the 32 bit sequence is 19h, 28h, AAh,
55h with each byte output LSB first. See Figure 11.
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