I2C send memory address in read operation

Question

Hello, 
 I'm trying to implement a comunication with a I2C device. I have a RA6M4 microcontroller and just one slave device on I2C. 
 The write operation seems to be good, as far the device has a expected behaviour. 
 But, in read operation, i can not fulfill the sequence of the device. The sequence is like a I2C read memory: 
 
 The point is: 
 - If I execute the read function (R_IIC_MASTER_Read), the start, device address, read bit, and acknoledge is good, but register address is always 0xFF, like a dummy byte. 
 - If I execute the write function, (R_IIC_MASTER_Write), the start and device address is good, but it sends always the write bit (0). 
 
 So, how can I achieve the correct sequence? No examples found that work it. 
 Thanks.

IK_Renesas · Accepted Answer

Hello David, 
 Apologies for my delayed response. 
 You mentioned that: 
 " "Since to read the contents of Reg0 which is 0x00 you first need to write to the slave the adress of the register you want to read." 
 NO. To read I just need to follow what the datasheet says:" 
 
 Please let me inform you that what you are describing does not comply with what the I2C protocol says. 
 Generally to read the contents of a specific register from the slave the write operation to the slave with writing the address of the register you want to get its contents, it is necessary before performing the read operation. 
 Please check the screenshot below: 
 
 As you can see from the figure I've send you above. In I2C protocol the steps to read the contents of a register of the slave device are: 
 START->7-bit slave Address->R/W=0(Write operation)->ACK->Register Address(1 byte)->ACK->Sr(Repeated Start)->7-bit slave Address->R/W=1 (Read Operation)->ACK->Data from Register-> NACK(from the slave since it does not have any more data to send)->STOP 
 And this application note to understand better the I2C: 
 Understanding the I2C Bus 
 
 What you are describing is not a read register operation. 
 Also the function readReg is made to read 2 bytes from slave have you changed the size to 1? 
 Also the Reg0 is the EN/RESET register of your datasheet so I think it's very important here to check what other processes have you done before reading the Reg0. Have you written any data on this register? 
 Please try to access the contents of an other register then Reg0 to check it's contents for example try to read Reg4 
 
 And see if you get the contents you have written to this register. 
 Also let me send you some screenshots from the results I get by using RA6M4 when I want to access register with adress 0x05 to read the raw temperature bytes from MCP9808 which is a temperature sensor. 
 As you can see first write is performed , I write to slave 0x05 which is the address of the register I want to read and then after 100 ms approximately since I have also some while loops checking for timeout I have the read process where I read the contents from this register.

Thank you! 
 Best Regards, 
 IK

IK_Renesas · Answer

Hello David, 
 Thanks for reaching out Renesas Engineering Community. 
 First of all I would suggest to you to advise the documentation of the r_iic_master module in FSP. 
 https://renesas.github.io/fsp/group___i_i_c___m_a_s_t_e_r.html 
 
 There is also an example code. 
 Also let me inform you that the IIC driver in FSP is a non blocking driver, which means that for example if your preform a Write operation 
 the R_IIC_Write() API will return immediately and you should declare a callback as this one shown below to get notified that your operation is actually completed even though it returns FSP_SUCCESS. 
 /* Callback function */
void g_i2c_master0_callback(i2c_master_callback_args_t *p_args)
{
 /* TODO: add your own code here */
 i2c_event=p_args->event;
}
 
 And check the value of the variable i2c_event. And check if it gets one this values below:

In order to find out what is going wrong we would like to have more information from you like your configurations for I2C and some sample code. 
 
 However let me attach for you an example for I2C that worked for me for reading an I2C temperature sensor. Notice that the example might be forEK-RA2L1 but nothing changes as far as it concerns the code, only set your own slave address and of course change the configurations for EK-RA6M4 for the I2C stack (pins, channels etc.). 
 Hope this helps. 
 Best Regards, 
 IK 
 
 5355.i2c_masterEK_RA2L1.zip

I2C send memory address in read operation

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