LSM9DS1 - IO Pins

[Dave Kearney]

Posted on September 21, 2017 at 07:14

Hi Guys, I'm planning on using the LSM9DS1 as a heading sensor on my board, and I was curious about the functionality of some of the pins - I couldn't find any detailed description in the datasheet.

The pin description describes Pins 5,6 (SDO_A/G, SDO_M) as 'I2C least significant bit of the device address' for I2C mode - are these required if talking to the module in I2C mode?

Also am I correct in assuming that pins 7,8 (CS_A/G, CS_M) just need to be pulled high externally to VDD_IO to enable I2C mode?

And are pins 9 - 13 required or is it possible to just use the I2C bus to talk to the module and read back measurements etc? I'm guessing the interrupts would be handy to alert to a fall or something like that but would not necessarily be required? And I'm not sure the purpose of the Data Ready, Data Enable Pins?

Many Thanks in advance!

Dave

#lsm9ds1

[Miroslav BATEK]

Posted on October 24, 2017 at 16:20

Yes, in example two LSM9DS1 connected to the same I2C bus.

Only two 7-bit addresses are possible 1101010b = 0x6A or 1101011b = 0x6B, the last bit is set by the connection

SDO_A/G pin.

[Dmitrij Gendler]

Posted on October 24, 2017 at 16:45

Thank you.

Will you be so kind as to answer another question ?

I have the address of I2C 0x6A. I want ot read WHO_AM_I (0x0F) and STATUS_REG(0x17)

Is it neccessary to set many control registers for accelerometer or only some of them ?

My try gives me only nulls in both of them.

[Miroslav BATEK]

Posted on October 25, 2017 at 09:51

You don't have to set any register to be able to read any sensor register.

Read 

WHO_AM_I (0x0F) register is good start to check your sensor connection and I2C settings is correct.

If you read zeros then you have something wrong.

[Dmitrij Gendler]

Posted on October 25, 2017 at 11:53

Thanks you very much. 

Some questions more.

1. 

Sub-address

Manual says:

In the I2C of the accelerometer and gyroscope sensor, after the start condition (ST) a slave address is sent, once a slave acknowledge (SAK) has been returned, an 8-bit sub-address (SUB) is transmitted.

8-bit sub-address (SUB) – register address ?

1. 2 

   Slave address.

In table 15 in order to read one byte from sensor:

ST   SAD+W   SAK   SUB   SAK

I have    SAD[6:1] = 0x6A

SAD+W – 7-bit slave address without SA0 ?

I.e., I have I2C address   110101 = 0x6A

7-bit     SAD[6:1] + W = 110101 + 0 = 0x6A

Or

SA0 must be taken into account too and then, if SA0 = 0,

8-bit     SAD[6:1] + SA0 + W = 110101 + 0 + 0 = 0xD4

[Dmitrij Gendler]

Posted on October 25, 2017 at 12:45

Miroslav, thank you for your answers.

I‘ve succeeded to read the register WHO_AM_I. IMHO the description is not clear.

I write here code for c♯ and IoT.

I2cDevice

i2cDevAccel – c♯ object for communication channel I2C.

//I2C sensor address = 0x6A

//7-bit slave address SAD[6:1] + write -> 0x6A + 0 -> 0xD4

byte

[] buf1 =

new

byte

[] { 0xd4 };

//address of register WHO_AM_I = 0x0F

byte

[] buf2 =

new

byte

[] { WHO_AM_I };

//result of reading

byte

[] buf3 =

new

byte

[1];

            i2cDevAccel.Write(buf1);

            i2cDevAccel.WriteRead(buf2, buf3);

Result in buf3 must be equal to 0x68.

Once more thank you very much.