LPS22DF datasheet(24/54 Pages) STMICROELECTRONICS

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7.3

SPI bus interface (CS = low)

The LPS22DF SPI is a bus slave. The SPI allows writing to and reading from the registers of the device.

The serial interface interacts with the application using 4 wires: CS, SPC, SDI and SDO.

Figure 16. Read and write protocol

SPC

SDI

SDO

AD5 AD4 AD3 AD2 AD1 AD0

DI7 DI6 DI5 DI4 DI3 DI2 DI1 DI0

DO7 DO6 DO5 DO4 DO3 DO2 DO1 DO0

AD6

CS enables the serial port and it is controlled by the SPI master. It goes low at the start of the transmission and

returns to high at the end. SPC is the serial port clock and it is controlled by the SPI master. It is stopped high

when CS is high (no transmission). SDI and SDO are respectively the serial port data input and output. Those

lines are driven at the falling edge of SPC and should be captured at the rising edge of SPC.

Both the read register and write register commands are completed in 16 clock pulses or multiples of 8 in the case

of multiple read/write bytes. Bit duration is the time between two falling edges of SPC. The first bit (bit 0) starts at

the first falling edge of SPC after the falling edge of CS while the last bit (bit 15, bit 23,...) starts at the last falling

edge of SPC just before the rising edge of CS.

bit 0: RW bit. When 0, the data DI(7:0) is written into the device. When 1, the data DO(7:0) from the device is

read. In the latter case, the chip will drive SDO at the start of bit 8.

bit 1-7: address AD(6:0). This is the address field of the indexed register.

bit 8-15: data DI(7:0) (write mode). This is the data that is written into the device (MSb first). bit 8-15: data

DO(7:0) (read mode). This is the data that is read from the device (MSb first). In multiple read/write commands

further blocks of 8 clock periods are added. When the IF_ADD_INC bit is 0, the address used to read/write

data remains the same for every block. When the IF_ADD_INC bit is 1, the address used to read/write data is

incremented at every block.

The function and the behavior of SDI and SDO remain unchanged.

LPS22DF

SPI bus interface (CS = low)

DS13316 - Rev 1

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