SPSB100 datasheet(58/213 Pages) STMICROELECTRONICS

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Figure 33. SPI signal description

The communication frame starts with the falling edge of the CSN (Communication Start). CLK has to be low.

The SDI data is then latched at all following rising CLK edges into the internal shift registers.

After Communication Start the SDO leaves high impedance state and present the MSB of the data shifted out to

the SDO. At all following falling CLK edges data 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 took place, the

requested operation according to the operating code is performed.

5.2.2

Communication protocol

5.2.2.1

SDI frame

The devices data-in frame consists of 32 bits (OpCode (2 bits) + address (6 bits) + data (20 bits) + CRC (4 bits)).

The first two received bits (MSB, MSB-1) contain the operation code which indicates the instruction to be

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.

Figure 34. SDI frame

OC1 OC0

OPCODE

ADDRESS

DATA Byte 2

DATA Byte 1

MSB

LSB

time

DATA Byte 3

time

CRC

SPSB100

Serial peripheral interface (SPI)

DS14640 - Rev 2

page 58/213

SPSB100 Datasheet(PDF) 58 Page - STMicroelectronics