How to pointer to a different register I2C communication

[Anonymous]

 Hi,

       

I have a current sense INA219 which I am communicating through I2C. I am able to communicate with it but only the first register of INA219. INA219 has several registers which contain different values. I would like to access those registers. Could you tell me how I can read from those registers. For example the shunt voltage read by the INA219 is saved in 0x01 register of the INA219.

       

Thanks,

   

Jerry

[ETRO_SSN583]

Basicaly you have an address to a register, a C pointer. Lets say you

   

have -

       

unsigned char regval = 0;

   

unsigned char *xPtr = 0x01;

       

Then to acess the next register

       

regval = *(xPtr + 1);

       

Regards, Dana.

[Anonymous]

Hi jjthefreako,

       

Since you are intending to read from the Shunt Voltage register, you'll first have to initialize the pointer to that location (0x01).

   

The procedure would be as follows:

   

1) Give a "Write" command with the appropriate slave address followed by the address of the register which you want to read from (0x01). Donot give a "Stop" command.

   

2) Give a Repeat Start. Now the pointer is pointing to register 0x01.

   

3) Now give a Read Command with the same Slave address. The two bytes hence read corresponds to the Shunt Voltage you are looking for.

[Anonymous]

Hi,

   

First off thank you dan and dasg for ur replies.

   

I tried the following code and several variations of it but I am still not able to read. Could you please tell me where I am going wrong? 

   

I2C_UDB_M_MasterSendStart(EZI2C_SLAVE_ADDR_current1+0x01, I2C_UDB_M_WRITE_XFER_MODE);

   

I2C_UDB_M_MasterSendRestart(EZI2C_SLAVE_ADDR_current1+0x01, I2C_UDB_M_READ_XFER_MODE);

   

 I2C_UDB_M_MasterReadBuf(EZI2C_SLAVE_ADDR_current1+0x01, (uint8 *) i2cBufferRead,2, I2C_UDB_M_MODE_COMPLETE_XFER);

   

while(0u == (I2C_UDB_M_MasterStatus() & I2C_UDB_M_MSTAT_RD_CMPLT))

   

{ /* Wait read to be completed */

   

}

   

Thanks,

   

Jerene

[Anonymous · Accepted solution]

Hi Jerene,

       

A simple code for reading the location 0x01 would look something like this:

       

#include<device.h>

   

#define SLAVE_ADDRESS  0x00           /* Give the appropriate Slave Address */

       

uint8 shunt_volt[1] = {0x01};    /* The address of the Shunt Voltage register */

   

uint8 read_value[2];                  /* To store the read value */

       

void main()

   

{

   

     I2C_Start();

   

     CyGlobalIntEnable();

   

     I2C_MasterWriteBuf(SLAVE_ADDRESS, shunt_volt, 1, I2C_MODE_NO_STOP); /* This sets the pointer to Shunt Voltage register whose address is 0x01 */

   

     while(I2C_MasterStatus() == I2C_MSTAT_XFER_INP); /* Waits till the transfer is complete */

   

     I2C_MasterReadBuf(SLAVE_ADDRESS, read_value, 2, I2C_MODE_REPEAT_START ); /* read_value will hold the two bytes read. This begins with a repeat start */

   

     while(I2C_MasterStatus() == I2C_MSTAT_XFER_INP); /* Waits till the transfer is complete */

   

}

[Anonymous]

Also not to forget, you have to use pull up resistors on the SCL and SDA lines.

   

You can find a sample project in Creator by right clicking on the I2C Component and selecting the "Find Example Project.."

       

For the code written in my previous post, I have assumed that I am using an I2C component with an instance name of I2C and is configured to operate in Master mode.

[Anonymous]

 That worked great. Thank you dasg