M95320-R datasheet(11/48 Pages) STMICROELECTRONICS

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M95320-W M95320-R M95320-DR

Connecting to the SPI bus

Doc ID 5711 Rev 14

11/48

Connecting to the SPI bus

All instructions, addresses and input data bytes are shifted in to the device, most significant

bit first. The Serial Data Input (D) is sampled on the first rising edge of the Serial Clock (C)

after Chip Select (S) goes low.

All output data bytes are shifted out of the device, most significant bit first. The Serial Data

Output (Q) is latched on the first falling edge of the Serial Clock (C) after the instruction

(such as the Read from Memory Array and Read Status Register instructions) have been

clocked into the device.

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 memory devices connected to an SPI bus master. Only

one memory device is selected at a time, so only one memory device drives the Serial Data

Output (Q) line at a time. The other memory devices are high impedance.

The pull-up resistor R (represented in Figure 4) ensures that a device is not selected if the

Bus Master leaves the S line in the high impedance state.

In applications where the Bus Master may leave all SPI bus lines in high impedance at the

same time (for example, if the Bus Master is reset during the transmission of an instruction),

the clock line (C) must be connected to an external pull-down resistor so that, if all

inputs/outputs become high impedance, the C line is pulled low (while the S line is pulled

high): this ensures 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 kΩ..

AI12836b

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

VCC

VSS

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