A3G4250D Просмотр технического описания (PDF) - STMicroelectronics

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A3G4250D

MEMS motion sensor: 3-axis digital output gyroscope

STMicroelectronics 

Digital interfaces

A3G4250D

Figure 16. Multiple byte SPI write protocol (2-byte example)

CS

SPC

SDI

DI7 DI6 DI5 DI4 DI3 DI2 DI1 DI0 DI15 DI14 DI13 DI12 DI11 DI10 DI9 DI8

RW

MS AD5 AD4 AD3 AD2 AD1 AD0

5.2.3

Note:

SPI read in 3-wire mode

3-wire mode is entered by setting the SIM (SPI serial interface mode selection) bit to 1 in

CTRL_REG2.

Figure 17. SPI read protocol in 3-wire mode

CS

SPC

SDI/O

RW

DO7 DO6 DO5 DO4 DO3 DO2 DO1 DO0

MS AD5 AD4 AD3 AD2 AD1 AD0

The SPI read command is performed with 16 clock pulses:

Bit 0: READ bit. The value is 1.

Bit 1: MS bit. When 0, do not increment address; when 1, increment address in multiple

reading.

Bit 2-7: address AD(5:0). This is the address field of the indexed register.

Bit 8-15: data DO(7:0) (read mode). This is the data that is read from the device (MSb first).

The multiple read command is also available in 3-wire mode.

If the A3G4250D is used in a multi-SPI slave environment (several devices sharing the

same SPI bus), the accelerometer can be forced by software to remain in SPI mode. This

objective can be achieved by sending, at the beginning of the SPI communication, the

following sequence to the device:

a = read(0x05)

write(0x05, (0x20 OR a))

The programming of this register makes it possible to enhance the robustness of the SPI

system.

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Doc 022768 Rev 3

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