Micron M25P40 Serial Flash Embedded Memory
READ ELECTRONIC SIGNATURE
READ ELECTRONIC SIGNATURE
Once the device enters DEEP POWER-DOWN mode, all commands are ignored except
READ ELECTRONIC SIGNATURE and RELEASE from DEEP POWER-DOWN. Executing
either of these commands takes the device out of the DEEP POWER-DOWN mode.
The READ ELECTRONIC SIGNATURE command is entered by driving chip select (S#)
LOW, followed by the command code and three dummy bytes on serial data input
(DQ0) . Each bit is latched in on the rising edge of serial clock C. The 8-bit electronic
signature is shifted out on serial data output DQ1 on the falling edge of C; S# must be
driven LOW the entire duration of the sequence for the electronic signature to be read.
However, driving S# HIGH after the command code, but before the entire 8-bit electron-
ic signature has been output for the first time, still ensures that the device is put into
STANDBY mode.
Except while an ERASE, PROGRAM, or WRITE STATUS REGISTER cycle is in progress,
the READ ELECTRONIC SIGNATURE command provides access to the 8-bit electronic
signature of the device, and can be applied even if DEEP POWER-DOWN mode has not
been entered. The READ ELECTRONIC SIGNATURE command is not executed while an
ERASE, PROGRAM, or WRITE STATUS REGISTER cycle is in progress and has no effect
on the cycle in progress.
The READ ELECTRONIC SIGNATURE command is terminated by driving S# high after
the electronic signature has been read at least once. Sending additional clock cycles C
while S# is driven LOW causes the electronic signature to be output repeatedly.
If S# is driven HIGH, the device is put in STANDBY mode immediately unless it was pre-
viously in DEEP POWER-DOWN mode. If previously in DEEP POWER-DOWN mode, the
device transitions to STANDBY mode with delay as described here. Once in STANDBY
mode, the device waits to be selected so that it can receive, decode, and execute instruc-
tions.
• If S# is driven HIGH before the electronic signature is read, transition to STANDBY
mode is delayed by tRES1, as shown in the RELEASE from DEEP POWER-DOWN com-
mand sequence. S# must remain HIGH for at least tRES1(max).
• If S# is driven HIGH after the electronic signature is read, transition to STANDBY
mode is delayed by tRES2. S# must remain HIGH for at least tRES2(max).
Figure 20: READ ELECTRONIC SIGNATURE Command Sequence
0
C
7
8
C
x
RES2
t
LSB
DQ0
MSB
D
OUT
MSB
Dummy cycles
Deep Power-Down
D
OUT
D
OUT
Electronic Signature
D
OUT
D
OUT
D
OUT
D
OUT
LSB
D
OUT
Command
DQ1
High-Z
Standby
Don’t Care
Note:
1. Cx = 7 + (A[MAX] + 1).
PDF: 09005aef8456654f
m25p40.pdf - Rev. Y 8/12 EN
33
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