SensorsのトピックRe: MAG 3110 ctrl_reg2 reading issue.

MAG 3110 ctrl_reg2 reading issue.

nicolasdecroze — Tue, 03 Feb 2026 22:18:46 GMT

Hello,

I try to use MAG3110 sensor with an arduino due board.

I have a problem when i want to write in the "Ctrl_reg2" register.

I want to write 0x80 in the register but when i read it (just to verify), the register value is 0x00...

I haven't this issue with ctrl_reg1.

Here ou can see the writing code :

Wire.beginTransmission(MAG_ADDR); // transmit to device 0x0E

Wire.write(0x10); // ctrl register1

Wire.write(0x00); // Standby

Wire.endTransmission(); // stop transmitting

delay(15);

Wire.beginTransmission(MAG_ADDR); // transmit to device 0x0E

Wire.write(0x11); // ctrl register2

Wire.write(0x80); // send 0x80, enable auto resets

Wire.endTransmission(); // stop transmitting

Is there any special things to do with this register ?

Many thanks for the help.

Re: MAG 3110 ctrl_reg2 reading issue.

TomasVaverka — Wed, 20 Jan 2016 08:45:06 GMT

Hi Nicolas,

This is correct behaviour, the AUTO_MRST_EN is a write-only bit and always reads back as 0.

Let me know if you have any other questions.

Regards,

Tomas

PS: If my answer helps to solve your question, please mark it as "Correct". Thank you.

Re: MAG 3110 ctrl_reg2 reading issue.

nicolasdecroze — Tue, 09 Feb 2016 08:52:13 GMT

hi Tomas,

Sorry for late reply, i was in vacation :smileyhappy:

Many thanks for your help !

However i have one more question :

If RAW bit is 1, output data should be beetween -20000 and +20000 is that right?

Because when i put this bit to 1, output values are still beetween -32768 and +32768... is that normal ? or i have an issue in my software?

Regards,

Nicolas

Re: MAG 3110 ctrl_reg2 reading issue.

TomasVaverka — Tue, 09 Feb 2016 09:55:40 GMT

Hi Nicolas,

Having such big values is not normal, unless the device is exposed to strong magnetic fields. Could you please share here your source code and raw values you read from registers 0x01 – 0x06? There may be a problem with converting raw values to signed 16-bit numbers or with incorrect interpreting on output device (if used).

Regards,

Tomas

Re: MAG 3110 ctrl_reg2 reading issue.

nicolasdecroze — Wed, 09 Mar 2016 14:06:54 GMT

hi Tomas,

I'm really sorry for late reply but i had a big issue on another project so i hadn't a lot of time...

you can see below my Arduino source code :

I can see if there is a mistake...

Many thanks for your help.

regards,

Nicolas.

#include <Wire.h>

#define MAG_ADDR 0x0E // 7-bit address for the MAG3110, doesn't change

void setup()

{

pinMode(38, INPUT);

Serial.begin(115200); // start serial for output

Wire.begin(); // join i2c bus (address optional for master)

config(); // turn the MAG3110 on

}

void loop()

{

if (digitalRead(38) == HIGH){

print_values();

}

void config(void)

{

Wire.beginTransmission(MAG_ADDR); // transmit to device 0x0E

Wire.write(0x10); // ctrl register1

Wire.write(0x00); // Standby

Wire.endTransmission(); // stop transmitting

delay(15);

Wire.beginTransmission(MAG_ADDR); // transmit to device 0x0E

Wire.write(0x11); // ctrl register2

Wire.write(0x80); // send 0x80, enable auto resets

Wire.endTransmission(); // stop transmitting

delay(15);

Wire.beginTransmission(MAG_ADDR); // transmit to device 0x0E

Wire.write(0x11); // ctrl register2

Wire.write(0x30); // send 0x80, enable auto resets

Wire.endTransmission(); // stop transmitting

delay(15);

Wire.beginTransmission(MAG_ADDR); // transmit to device 0x0E

Wire.write(0x10); // ctrl register1

Wire.write(0xC9); // send 0x01, active mode

Wire.endTransmission(); // stop transmitting

}

void print_values(void)

{

int LSB_MASK = 0x00FF;

Serial.write(0x01);

int16_t X_T = readx();

Serial.write(X_T>>8); // MSB

Serial.write(X_T & LSB_MASK); // LSB

int16_t Y_T = ready();

Serial.write(Y_T>>8); // MSB

Serial.write(Y_T & LSB_MASK); // LSB

int16_t Z_T = readz();

Serial.write(Z_T>>8); // MSB

Serial.write(Z_T & LSB_MASK); // LSB

Serial.write(0x02);

}

//////////////////////////////// Read X /////////////////////////////////////

int16_t readx(void)

{

byte xl = 0;

byte xh = 0; // define the MSB and LSB

int16_t xout = 0;

Wire.beginTransmission(MAG_ADDR); // transmit to device 0x0E

Wire.write(0x01); // x MSB reg

Wire.endTransmission(); // stop transmitting

delayMicroseconds(2); // needs at least 1.3us free time between start and stop

Wire.requestFrom(MAG_ADDR, 1); // request 1 byte

while(Wire.available()) // slave may send less than requested

{

xh = Wire.read(); // receive the byte

}

delayMicroseconds(2); // needs at least 1.3us free time between start and stop

Wire.beginTransmission(MAG_ADDR); // transmit to device 0x0E

Wire.write(0x02); // x LSB reg

Wire.endTransmission(); // stop transmitting

delayMicroseconds(2); // needs at least 1.3us free time between start and stop

Wire.requestFrom(MAG_ADDR, 1); // request 1 byte

while(Wire.available()) // slave may send less than requested

{

xl = Wire.read(); // receive the byte

}

//xl = 0; // Ici on met le lsb à 0 pour éviter les fluctuations

xout = (xl|(xh << 8)); // concatenate the MSB and LSB

return xout;

}

//////////////////////////////// Read Y /////////////////////////////////////

int16_t ready(void)

{

byte yl = 0;

byte yh = 0; // define the MSB and LSB

int16_t yout = 0;

Wire.beginTransmission(MAG_ADDR); // transmit to device 0x0E

Wire.write(0x03); // y MSB reg

Wire.endTransmission(); // stop transmitting

delayMicroseconds(2); // needs at least 1.3us free time between start and stop

Wire.requestFrom(MAG_ADDR, 1); // request 1 byte

while(Wire.available()) // slave may send less than requested

{

yh = Wire.read(); // receive the byte

}

delayMicroseconds(2); // needs at least 1.3us free time between start and stop

Wire.beginTransmission(MAG_ADDR); // transmit to device 0x0E

Wire.write(0x04); // y LSB reg

Wire.endTransmission(); // stop transmitting

delayMicroseconds(2); // needs at least 1.3us free time between start and stop

Wire.requestFrom(MAG_ADDR, 1); // request 1 byte

while(Wire.available()) // slave may send less than requested

{

yl = Wire.read(); // receive the byte

}

//yl = 0; // Ici on met le lsb à 0 pour éviter les fluctuations

yout = (yl|(yh << 8)); // concatenate the MSB and LSB

return yout;

}

//////////////////////////////// Read Z /////////////////////////////////////

int16_t readz(void)

{

byte zl = 0;

byte zh = 0; // define the MSB and LSB

int16_t zout = 0;

Wire.beginTransmission(MAG_ADDR); // transmit to device 0x0E

Wire.write(0x05); // z MSB reg

Wire.endTransmission(); // stop transmitting

delayMicroseconds(2); // needs at least 1.3us free time between start and stop

Wire.requestFrom(MAG_ADDR, 1); // request 1 byte

while(Wire.available()) // slave may send less than requested

{

zh = Wire.read(); // receive the byte

}

delayMicroseconds(2); // needs at least 1.3us free time between start and stop

Wire.beginTransmission(MAG_ADDR); // transmit to device 0x0E

Wire.write(0x06); // z LSB reg

Wire.endTransmission(); // stop transmitting

delayMicroseconds(2); // needs at least 1.3us free time between start and stop

Wire.requestFrom(MAG_ADDR, 1); // request 1 byte

while(Wire.available()) // slave may send less than requested

{

zl = Wire.read(); // receive the byte

}

//zl = 0; // Ici on met le lsb à 0 pour éviter les fluctuations

zout = (zl|(zh << 8)); // concatenate the MSB and LSB

return zout;

}

//////////////////////////////// Read CTRL_REG_2 /////////////////////////////////////

byte readctrl2(void)

{

byte CTRL2; // define the MSB and LSB

Wire.beginTransmission(MAG_ADDR); // transmit to device 0x0E

Wire.write(0x11); // z MSB reg

Wire.endTransmission(); // stop transmitting

delayMicroseconds(2); // needs at least 1.3us free time between start and stop

Wire.requestFrom(MAG_ADDR, 1); // request 1 byte

while(Wire.available()) // slave may send less than requested

{

CTRL2 = Wire.read(); // receive the byte

}

return CTRL2;

}

//////////////////////////////// Read CTRL_REG_1 /////////////////////////////////////

byte readctrl1(void)

{

byte CTRL1; // define the MSB and LSB

Wire.beginTransmission(MAG_ADDR); // transmit to device 0x0E

Wire.write(0x10); // z MSB reg

Wire.endTransmission(); // stop transmitting

delayMicroseconds(2); // needs at least 1.3us free time between start and stop

Wire.requestFrom(MAG_ADDR, 1); // request 1 byte

while(Wire.available()) // slave may send less than requested

{

CTRL1 = Wire.read(); // receive the byte

}

return CTRL1;

}