A3G4250D Просмотр технического описания (PDF) - STMicroelectronics

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A3G4250D

MEMS motion sensor: 3-axis digital output gyroscope

STMicroelectronics 

A3G4250D

Digital interfaces

Table 15. Transfer when master is writing multiple bytes to slave

Master ST SAD + W

SUB

DATA

DATA

SP

Slave

SAK

SAK

SAK

SAK

Table 16. Transfer when master is receiving (reading) one byte of data from slave

Master ST SAD + W

SUB

SR SAD + R

NMAK SP

Slave

SAK

SAK

SAK DATA

Table 17. Transfer when master is receiving (reading) multiple bytes of data from slave

Master ST SAD+W

SUB

SR SAD+R

MAK

MAK

NMAK SP

Slave

SAK

SAK

SAK DATA

DATA

DATA

Data are transmitted in byte format (DATA). Each data transfer contains 8 bits. The number

of bytes transferred per transfer is unlimited. Data is transferred with the most significant bit

(MSb) first. If a receiver cannot receive another complete byte of data until it has performed

some other function, it can hold the clock line SCL LOW to force the transmitter into a wait

state. Data transfer only continues when the receiver is ready for another byte and releases

the data line. If a slave receiver does not acknowledge the slave address (i.e., it is not able

to receive because it is performing some real-time function) the data line must be left HIGH

by the slave. The master can then abort the transfer. A LOW to HIGH transition on the SDA

line while the SCL line is HIGH is defined as a STOP condition. Each data transfer must be

terminated by the generation of a STOP (SP) condition.

In order to read multiple bytes, it is necessary to assert the most significant bit of the sub-

address field. In other words, SUB(7) must be equal to 1, while SUB(6-0) represents the

address of the first register to be read.

In the presented communication format, MAK is “master acknowledge” and NMAK is “no

master acknowledge”.

5.2

SPI bus interface

The SPI is a bus slave. The SPI allows writing and reading of the device registers. The serial

interface interacts with the external world through 4 wires: CS, SPC, SDI, and SDO.

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