M25P64-VMF6TP datasheet(36/49 Pages) STMICROELECTRONICS

36 / 49 page

Instructions

M25P64

36/49

6.11

Read Electronic Signature (RES)

The instruction is used to read, on Serial Data Output (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) instruction. The old-style Electronic

Signature is supported 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 Signature, stored in the memory, is

shifted out on Serial Data Output (Q), each bit being shifted out during the falling edge of

Serial Clock (C).

The instruction sequence is shown in Figure 18.

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 repeatedly.

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 selected, so that it can receive, decode and

execute instructions.

Driving Chip Select (S) High after the 8-bit instruction byte has been received by the device,

but before 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 execute

instructions.

Figure 18.

Read Electronic Signature (RES) instruction sequence and data-out

sequence

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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