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I2C on original netduino not reading multiple bytes

Started by h3mp, Feb 17 2015 10:21 PM
I2C LSM9DS0

Best Answer TheIceManProgrammeth, 21 February 2015 - 11:02 PM

I had the same issue. Try amending:

 

byte write = { AddressOfFirstRegisterIneed };

 

to

 

byte write = { AddressOfFirstRegisterIneed | (1 << 7) };

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#1 h3mp

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Posted 17 February 2015 - 10:21 PM

I'm new to I2C so apologies in advance  :D

 

I'm trying to read multiple registers at once from a LSM9DS0 accelerometer/gyro/compass chip..

 

Each sensor has 6 registers in a row that return X/Y/Z high and low bytes.. so i should be able to use the I2C_ADDRESS of the chip's XM sensor, then point a 'read' at the first of the 6 registers then i was hoping that would return an array of that register plus the next 5..

 

I use code based on this following example i found on the web:

I2CDevice.Configuration config = new I2CDevice.Configuration(I2C_ADDRESS, I2C_CLOCK_RATE_KHZ);
I2CDevice i2c = new I2CDevice(config);

byte write = { AddressOfFirstRegisterIneed };
byte read = new byte[6]; //surely this should return the first and subsequent 5 registers?
// create I2C write and read transaction
I2CDevice.I2CTransaction i2cTx = new I2CDevice.I2CTransaction[2];
i2cTx[0] = I2CDevice.CreateWriteTransaction(write);
i2cTx[1] = I2CDevice.CreateReadTransaction(read);
// execution
i2c.Execute(i2cTx, I2C_TIMEOUT);

 

..what i get back is an array of bytes all containing the same value!? (there should be 6 distinct values returned).

 

if i do 6 separate transactions one after another reading just 1 byte, then i can return all 6 registers successfully..

 

but as they are all in a row should i not be able to do all this in one transaction?  :wacko:

 

(i'm doing this on my old Netduino 1 that is probably running 4.2.0 update1 as i didnt have any newer netduinos in my office today)

 

 

 


#2 CW2

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Posted 21 February 2015 - 07:58 PM

You'd need special I2C methods that support repeated-start condition, as described in http://forums.netdui...rt-bit-support/


#3 TheIceManProgrammeth

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Posted 21 February 2015 - 11:02 PM   Best Answer

I had the same issue. Try amending:

 

byte write = { AddressOfFirstRegisterIneed };

 

to

 

byte write = { AddressOfFirstRegisterIneed | (1 << 7) };


#4 h3mp

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Posted 22 February 2015 - 01:38 PM

Thanks IceMan..

 

I had missed that in the datasheet.. it states:

 

 

“The I2C embedded inside the LSM9DS0 behaves like a slave device and the following protocol must be adhered to. After the start condition (ST) a slave address is sent, once a slave acknowledge (SAK) has been returned, an 8-bit sub-address (SUB) will be transmitted: the 7 LSb represents the actual register address while the MSB enables the address auto increment. If the MSb of the SUB field is ‘1’, the SUB (register address) will be automatically increased to allow multiple data read/writes.”

 

so or'ing in the MSB 1 works great thanks  :D


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