3 read sector lockdown registers – Rainbow Electronics AT25DQ321 User Manual
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AT25DQ321 [DATASHEET]
8718D–DFLASH–12/2012
10.3 Read Sector Lockdown Registers
The Sector Lockdown Registers can be read to determine the current lockdown status of each physical 64KB sector. To
read the Sector Lockdown Register for a particular 64KB sector, the CS pin must first be asserted and the opcode of 35h
must be clocked in. Once the opcode has been clocked in, three address bytes designating any address within the 64KB
sector must be clocked in. After the address bytes have been clocked in, data will be output on the SO pin during every
subsequent clock cycle. The data being output will be a repeating byte of either FFh or 00h to denote the value of the
appropriate Sector Lockdown Register.
At clock frequencies above f
CLK
, the first byte of data output will not be valid. Therefore, if operating at clock frequencies
above f
CLK
, at least two bytes of data must be clocked out from the device in order to determine the correct status of the
appropriate Sector Lockdown Register.
Table 10-2. Read Sector Lockdown Register - Output Data
Deasserting the CS pin will terminate the read operation and put the SO pin into a high-impedance state. The CS pin can
be deasserted at any time and does not require that a full byte of data be read.
Figure 10-3. Read Sector Lockdown Register
Output Data
Sector Lockdown Register Value
00h
Sector Lockdown Register Value is 0 (Sector is Not Locked Down).
FFh
Sector Lockdown Register Value is 1 (Sector is Permanently Locked Down).
SO
SI
SCK
CS
MSB
MSB
2
3
1
0
0
0
1
1
0
1
0
1
6
7
5
4
10 11
9
8
12
39
42 43
41
40
37 38
33
36
35
34
31 32
29 30
44
47 48
46
45
Opcode
A
A
A
A
A
A
A
A
A
MSB
X
X
X
X
X
X
X
X
MSB
MSB
D
D
D
D
D
D
D
D
D
D
Address Bits A23-A0
Don't Care
Data Byte
High-impedance