SPSB0813 datasheet(43/135 Pages) STMICROELECTRONICS

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Figure 27. SPI signal description

The communication frame starts with the falling edge of the CSN (communication start). SCK has to be low.

The SDI data is then full latched following the rising SCK edges into the internal shift registers.

After communication start the SDO leaves 3-state mode and presents the MSB of the data shifted out to SDO, it

is then full latched following the falling SCK edges data and it is shifted out through the internal shift registers to

SDO.

The communication frame is finished with the rising edge of CSN. If a valid communication has taken place (for

example, correct number of SCK cycles, access to a valid address), the requested operation according to the

operating code will be performed (write or clear operation).

4.2.2

Communication protocol

4.2.2.1

SDI frame

The devices data-in frame consists of 32 bits (OpCode (2 bits) + address (6 bits) + data byte 3 + data byte 2 +

data byte 1).

The first two transmitted bits (MSB, MSB-1) contain the operation code which represents the instruction, which is

performed. The following 6 bits (MSB-2 to MSB-7) represent the address on which the operation is performed.

The subsequent bytes contain the payload.

SPSB081

Signal description

DS14048 - Rev 1

page 43/135

SPSB0813 データシート(PDF) 43 Page - STMicroelectronics