M25PX32-VMP6F datasheet(11/63 Pages) STMICROELECTRONICS

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M25PX32

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 5, is the clock polarity when the

bus master is in Standby mode and not transferring data:

●

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

●

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

Figure 4.

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.

Figure 4 shows an example of three devices connected to an MCU, on an SPI bus. Only one

device is selected at a time, so only one device drives the Serial Data output (DQ1) line at a

time, the other devices are high impedance. Resistors R (represented in Figure 4) ensure

that the M25PX32 is 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 (for example, 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, the S line is pulled High while the C line 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). The

typical value of R is 100 k

Ω, assuming that the time constant R*C

p (Cp = parasitic

capacitance of the bus line) is shorter than the time during which the Bus Master leaves the

SPI bus in high impedance.

AI13725b

SPI Bus Master

SPI memory

device

SDO

SDI

SCK

DQ1DQ0

SPI memory

device

DQ1 DQ0

SPI memory

device

DQ1DQ0

CS3

CS2 CS1

SPI interface with

(CPOL, CPHA) =

(0, 0) or (1, 1)

HOLD

VCC

VSS

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