LSM6DSM datasheet(40/113 Pages) STMICROELECTRONICS

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Digital interfaces

LSM6DSM

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DocID028165 Rev 2

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 function, 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 doesn’t 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 left 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 the presented communication format MAK is Master acknowledge and NMAK is No

Master Acknowledge.

6.5

SPI bus interface

The LSM6DSM SPI is a bus slave. The SPI allows writing and reading the registers of the

device.

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

Figure 11. 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 goes back 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 in

multiples of 8 in 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 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).

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