LSM303AGR datasheet(38/68 Pages) STMICROELECTRONICS

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Digital interfaces

LSM303AGR

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DocID027765 Rev 5

(MSb) first. If a receiver can’t 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 doesn’t 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 the presented communication format MAK is Master acknowledge and NMAK is No

Master Acknowledge.

Default address:

The accelerometer sensor slave address is 0011001b while magnetic sensor slave address

is 0011110b.

The slave addresses are completed with a Read/Write bit. If the bit was ‘1’ (Read), a

repeated START (SR) condition must be issued after the two sub-address bytes. If the bit is

‘0’ (Write) the master will transmit to the slave with direction unchanged. Table 23 and

Table 24 explain how the SAD+Read/Write bit patterns are composed, listing all the

possible configurations.

Linear acceleration sensor: the default (factory setting) 7-bit slave address is

0011001b.

Table 23. SAD + Read/Write patterns

Magnetic field sensor: the default (factory setting) 7-bit slave address is 0011110b.

Table 24. SAD + Read/Write patterns

6.2

SPI bus interface

The LSM303AGR SPI is a bus slave. The SPI allows writing and reading the registers of the

device.

The serial interface interacts with the application using 3 wires: CS_XL or CS_MAG, SPC,

SDI/O.

Command

SAD[6:0]

R/W

SAD + R/W

Read

0011001

00110011 (33h)

Write

0011001

00110010 (32h)

Command

SAD[6:0]

R/W

SAD + R/W

Read

0011110

00111101 (3Dh)

Write

0011110

00111100 (3Ch)

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