LSM330D Datasheet, PDF (35/66 Pages) STMicroelectronics – Low power mode

LSM330D
Digital interfaces
6.2
SPI bus interface
The LSM330D SPI is a bus slave. The SPI allows writing and reading the registers of the
device.
The serial interface interacts with the outside world through 4 wires: CS, SPC, SDI and SDO
(SPC, SDI, SD0 are common).
Figure 14. Read and write protocol
CS
SPC
SDI
RW
DI7 DI6 DI5 DI4 DI3 DI2 DI1 DI0
MS AD5 AD4 AD3 AD2 AD1 AD0
SDO
DO7 DO6 DO5 DO4 DO3 DO2 DO1 DO0
AM10129V1
CS is the serial port enable and is controlled by the SPI master. It goes low at the start of the
transmission and returns high at the end. SPC is the serial port clock and 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. These 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-byte read/write. 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 to the device. When 1, the data DO(7:0)
from the device is read. In the latter case, the chip drives SDO at the start of bit 8.
bit 1: MS bit. When 0, the address remains 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 will be written to the device (MSb
first).
bit 8-15: data DO(7:0) (Read mode). This is the data that will be 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 remain unchanged.
Doc ID 022562 Rev 2
35/66