M25P64
Read Electronic Signature (RES)
The instruction is used to read, on Serial Data Out-
put (Q), the old-style 8-bit Electronic Signature,
whose value for the
M25P64
is
16h.
Please note that this is not the same as, or even a
subset of, the JEDEC 16-bit Electronic Signature
that is read by the Read Identifier (RDID) instruc-
tion. The old-style Electronic Signature is support-
ed for reasons of backward compatibility, only, and
should not be used for new designs. New designs
should, instead, make use of the JEDEC 16-bit
Electronic Signature, and the Read Identifier
(RDID) instruction.
The device is first selected by driving Chip Select
(S) Low. The instruction code is followed by 3
dummy bytes, each bit being latched-in on Serial
Data Input (D) during the rising edge of Serial
Clock (C). Then, the old-style 8-bit Electronic Sig-
nature, stored in the memory, is shifted out on Se-
rial Data Output (Q), each bit being shifted out
during the falling edge of Serial Clock (C).
The instruction sequence is shown in
The Read Electronic Signature (RES) instruction
is terminated by driving Chip Select (S) High after
the Electronic Signature has been read at least
once. Sending additional clock cycles on Serial
Clock (C), while Chip Select (S) is driven Low,
cause the Electronic Signature to be output re-
peatedly.
When Chip Select (S) is driven High, the device is
put in the Standby Power mode. Once in the
Standby Power mode, the device waits to be se-
lected, so that it can receive, decode and execute
instructions.
Driving Chip Select (S) High after the 8-bit instruc-
tion byte has been received by the device, but be-
fore the whole of the 8-bit Electronic Signature has
been transmitted for the first time, still ensures that
the device is put into Standby Power mode. Once
in the Standby Power mode, the device waits to be
selected, so that it can receive, decode and exe-
cute instructions.
Figure 19. Read Electronic Signature (RES) Instruction Sequence and Data-Out Sequence
S
0
C
Instruction
3 Dummy Bytes
1
2
3
4
5
6
7
8
9 10
28 29 30 31 32 33 34 35 36 37 38
D
High Impedance
Q
23 22 21
MSB
3
2
1
0
Electronic Signature Out
7
MSB
6
5
4
3
2
1
0
AI04047C
Note: The value of the 8-bit Electronic Signature, for the M25P64, is 16h.
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