M25P20 datasheet(9/50 Pages) STMICROELECTRONICS

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M25P20

SPI modes

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SPI modes

These devices can be driven by a microcontroller with its SPI peripheral running in either of

the two following modes:

●

CPOL=0, CPHA=0

●

CPOL=1, CPHA=1

For these two modes, input data is latched in on the rising edge of Serial Clock (C), and

output data is available from the falling edge of Serial Clock (C).

The difference between the two modes, as shown in Figure 4, is the clock polarity when the

bus master is in Stand-by mode and not transferring data:

●

C remains at 0 for (CPOL=0, CPHA=0)

●

C remains at 1 for (CPOL=1, CPHA=1)

Figure 3.

Bus Master and memory devices on the SPI Bus

The Write Protect (W) and Hold (HOLD) signals should be driven, High or Low as appropriate.

These pull-up resistors, R, ensure that the memory devices are not selected if the Bus Master leaves the S line in the high-

impedance state. As the Bus Master may enter a state where all inputs/outputs are in high impedance at the same time

(e.g.: when the Bus Master is reset), the clock line (C) must be connected to an external pull-down resistor so that, when all

inputs/outputs become high impedance, S is pulled High while C is pulled Low (thus ensuring that S and C do not become

High at the same time, and so, that the tSHCH requirement is met).

AI12836

SPI Bus Master

SPI Memory

Device

SDO

SDI

SCK

CQD

SPI Memory

Device

CQD

SPI Memory

Device

CQD

CS3

CS2

CS1

SPI Interface with

(CPOL, CPHA) =

(0, 0) or (1, 1)

HOLD

R(2)

VCC

VSS

R(2)

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