M25P64-VMF6TP datasheet(25/38 Pages) STMICROELECTRONICS

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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 Figure 19.

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

Note: The value of the 8-bit Electronic Signature, for the M25P64, is 16h.

AI04047C

3456789 10

28 29 30 31 32 33 34 35

22 21

3210

36 37 38

765432

High Impedance

Electronic Signature Out

Instruction

3 Dummy Bytes

MSB

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