Digital interfaces

LPS331AP

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Doc ID 022112 Rev 7

Data are transmitted in byte format (DATA). Each data transfer contains 8 bits. The number

of bytes transferred per transfer is unlimited. Data is transferred with the most significant bit

(MSb) first. If a receiver can’t receive another complete byte of data until it has performed

some other functions, it can hold the clock line, SCL LOW to force the transmitter into a wait

state. Data transfer only continues when the receiver is ready for another byte and releases

the data line. If a slave receiver does not acknowledge the slave address (i.e. it is not able to

receive because it is performing some real time function) the data line must be kept HIGH by

the slave. The master can then abort the transfer. A LOW to HIGH transition on the SDA line

while the SCL line is HIGH is defined as a STOP condition. Each data transfer must be

terminated by the generation of a STOP (SP) condition.

In order to read multiple bytes incrementing the register address, it is necessary to assert

the most significant bit of the sub-address field. In other words, SUB(7) must be equal to 1

while SUB(6-0) represents the address of the first register to be read.

In the presented communication format MAK is Master acknowledge and NMAK is no

master acknowledge.

5.3

SPI bus interface

The LPS331AP SPI is a bus slave. The SPI allows to write and read the registers of the

device.

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

Figure 4.

Read and write protocol

CS is the serial port enable 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

Table 12.

Transfer when master is receiving (reading) one byte of data from slave

Master

ST

SAD + W

SUB

SR

SAD + R

NMAK

SP

Slave

SAK

SAK

SAK

DATA

Table 13.

Transfer when master is receiving (reading) multiple bytes of data from

slave

Master

ST

SAD+W

SUB

SR

SAD+R

MAK

MAK

NMAK

SP

Slave

SAK

SAK

SAK

DATA

DATA

DATA

CS

SPC

SDI

SDO

RW

AD5 AD4 AD3 AD2 AD1 AD0

DI7DI6 DI5DI4 DI3DI2 DI1DI0

DO7DO6 DO5DO4 DO3DO2 DO1DO0

MS