AN2335 datasheet(13/40 Pages) STMICROELECTRONICS

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AN2335

Digital interfaces

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4.2

SPI bus interface

The LIS302DL 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, SPDI and

SPDO.

4.2.1

Read & write protocol

Figure 4.

Read & write protocol

CS is the Chip Select 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 clocks pulses or

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

When 1, the address will be 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 into 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 MS

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

is 1 the address used to read/write data is incremented at every block.

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

SPC

SDI

SDO

AD5 AD4 AD3 AD2 AD1 AD0

DI7

DI6

DI5

DI4

DI3

DI2

DI1

DI0

DO7 DO6 DO5 DO4 DO3 DO2 DO1 DO0

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