I3G4250D Datasheet, PDF (27/43 Pages) STMicroelectronics – 3-axis digital output gyroscope

I3G4250D
Digital interfaces
5.2.3
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 (21h).
Figure 17. SPI read protocol in 3-wire mode
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The SPI read command is performed with 16 clock pulses:
Bit 0: READ bit. The value is 1.
Bit 1: MS bit. When 0, does not increment address; when 1, increments address in multiple
reads.
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).
A multiple read command is also available in 3-wire mode.
If the I3G4250D is used in a multi-SPI slave environment (several devices sharing the same
SPI bus), the gyroscope 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.
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