Electronic – GY-521 Unable to set PWR_MGMT_1 register – can’t disable SLEEP mode

8051accelerometergyroi2cmicrocontroller

I am attempting to interface between a custom 8051-based MCU and a new (ebay) GY-521 module (Gyro/Accel chip) using I2C bus. I have written the I2C bit-bang functions myself and they seem to be working fine. I can view bus operations (Read/write) on the scope, and I'm seeing ACKs from the GY-521 when they should be seen.

However, in order to read the gyro/accel data, I must clear the "SLEEP" bit from the PWR_MGMT_1 register.

Procedure:
1. Send START sequence
2. Send 7-bit address + WRITE bit (0)
3. Read ACK from slave
4. Write 8-bit register address (0x6b)
5. Read ACK
6. Write 8-bit data value (0x01 = use X Gyro as clock source)
7. Read ACK
8. Send STOP sequence.

I can watch the MCU write the new value (0x01) to the register, but then when I Read back the register, the value is back to 0x40 (default).

Any reads of the gyro or accel values return zeros due to the module being in sleep mode.

Here is the spec sheet for the MPU-6050 gyro that's used in this board.
https://www.cubby.com/pli/Spec+Sheet.pdf/_506bd71d53d3454282f06fa698666f04

Here's the register list:
https://www.cubby.com/pli/Register+Map.pdf/_17685da9808c42099c5ebdc1058c63b3

If you wish, I can post the scope output where you can see the value being set, the ACK received, and then reading back the value yielding the default.

Any suggestions appreciated.

Thanks

Best Answer

The PWR_MGMT_1 register should always be set the last after all the register configurations like that:

void MPU9150_Init_awake_SensorRegister(unsigned int MasterI2C_BaseAddress)

{

WriteByte_to_SlaveRegister(MasterI2C_BaseAddress,RA_GYRO_CONFIG,0x08); WriteByte_to_SlaveRegister(MasterI2C_BaseAddress,RA_ACCEL_CONFIG,0x10); WriteByte_to_SlaveRegister(MasterI2C_BaseAddress,RA_USER_CTRL,0x00); WriteByte_to_SlaveRegister(MasterI2C_BaseAddress,RA_PWR_MGMT_1,0x09);

}

I used 0x09 instead of 0x01 to disable the temperature sensor cuz I don't need it.
By the way, I just tried that and it works so far; I still need to experiment with it however.

Related Solutions

Electronic – I2C combining read and write operation

There is no way to do what you want and still follow the I2C protocol. The closest you can get is the "Repeated Start" condition. Even with a repeated start, you must send the address a second time to read.

"Repeated start" is used in the case of a multi-master system, and it allows a master to lock the bus and prevent it from being taken over by another master. Instead of issuing a stop bit, the master sends another start bit, and retains control of the bus until the stop bit is sent. In this way, you could call the repeated start a single "operation", even though multiple reads/writes can be performed.

In your theoretical protocol, how much speed do you think you'll gain by not issuing the address a second time? Is that time savings needed for your design?

Electronic – Msp430g2553 i2c communication library with itg3200 gyroscope

This question has been solved in Ti website and the following is the solution which he added:

From looking at the USCI Operation, I2C mode section in the MSP430x2xx >Family User's Guide SLAU144I I think the UCTXSTT bit will be cleared after >the slave has ACKed its receive address, and before the data has been read >from the slave. Therefore, the following in the Receive function could read >the UCB0RXBUF before the data has been received:
  while (UCB0CTL1 & UCTXSTT); // Start condition sent? RXBuffer full?
  receivedByte = UCB0RXBUF;
Try changing to:
 while((IFG2 & UCB0RXIFG) == 0); // Wait until data read

 receivedByte = UCB0RXBUF;
Chester Gillon's post

I fixed my problem by changing some parts in the Receive function. Thanks >to Chester Gillon's post, it made me realise that STT interrupt occurs >right after the slave ACK the master. After checking the user guide >carefully, i found this:

If a master wants to receive a single byte only, the UCTXSTP bit must be >set while the byte is being received. For this case, the UCTXSTT may be polled to determine when it is >cleared:

So this STOP condition must occur after the ACK but before the second data >ACK. So i changed my receive function into this and it solved all my >problems:
uint8_t Receive(char registerAddr){
uint8_t receivedByte = 0;
while (UCB0CTL1 & UCTXSTP); // Ensure stop condition got sent
UCB0CTL1 |= UCTR + UCTXSTT; // I2C start condition with UCTR flag for >     transmit
while((IFG2 & UCB0TXIFG) == 0); //UCB0TXIFG is set immidiately
UCB0TXBUF = registerAddr; //write registerAddr in TX buffer
while((IFG2 & UCB0TXIFG) == 0); // wait until TX buffer is empty and >     transmitted
UCB0CTL1 &= ~UCTR ; // Clear I2C TX flag for receive
UCB0CTL1 |= UCTXSTT; // I2C start condition with NACK for single byte >     reading
while (UCB0CTL1 & UCTXSTT); // Start condition sent? RXBuffer full?
UCB0CTL1 |= UCTXSTP;
while((IFG2 & UCB0RXIFG) == 0); // wait until TX buffer is empty and >     transmitted
receivedByte = UCB0RXBUF; // I2C stop condition
return receivedByte;
}
Barışcan Kayaoğlu's post

https://e2e.ti.com/support/microcontrollers/msp430/f/166/t/265825

Best Answer

Related Solutions

Electronic – I2C combining read and write operation

Electronic – Msp430g2553 i2c communication library with itg3200 gyroscope

Chester Gillon's post

Barışcan Kayaoğlu's post

Related Topic