LSM6DSM Datasheet, PDF (40/113 Pages) STMicroelectronics – always-on 3D accelerometer and 3D gyroscope

Digital interfaces
LSM6DSM
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
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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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