LSM9DS1 datasheet(34/72 Pages) STMICROELECTRONICS

34 / 72 page

Digital interfaces

LSM9DS1

34/72

DocID025715 Rev 3

5.3

Magnetic sensor SPI bus interface

The LSM9DS1 magnetic sensor SPI is a bus slave. The SPI allows writing and reading the

registers of the device.

The serial interface connects to applications using 4 wires: CS_M, SPC, SDI and SDO_M.

Figure 22. Magnetic sensor read and write protocol

CS_M 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_M is high (no transmission). SDI

and SDO_M 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_M while the last bit (bit 15, bit 23, ...) starts at the last falling edge of SPC just before

the rising edge of CS_M.

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_M at the start of bit 8.

bit 1: MS bit. When 0, the address will remain unchanged in multiple read/write commands.

When 1, the address is auto-incremented in multiple read/write commands.

bit 2-7: address AD(5:0). 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 will be added. When the

MS bit is ‘0’, the address used to read/write data remains the same for every block. When

the MS bit is ‘1’, the address used to read/write data is increased at every block.

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

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