topic Re: I2C receive problem with KL25Z in Kinetis Microcontrollers

I2C receive problem with KL25Z

rothkarl — Sun, 04 Aug 2013 11:20:06 GMT

Dear Freescale Community!

I've successfully set up a toolchain to program the KL25Z dev board, and I need some kind of help using I2C!

I'am trying to access the onboard inertia sensor, I can address it correctly, I receive ACK on my commands, but when I want to receive data, I cannot get the proper data back.

Example: I want to read out the "Who I am" register, the chip accepts my request, but I cannot get back the 0x2A result, as I should. Here is my code:

I2C0_F |= I2C_F_MULT(0); //erata says MULT with different value of 0 blocks RESTART condition

I2C0_F |= I2C_F_ICR(63); //~317 kbaud

I2C0_C1 |= I2C_C1_IICEN_MASK;//enable I2C module

I2C0_C1 |= I2C_C1_TX_MASK;//set up for transmit

I2C0_C1 |= I2C_C1_MST_MASK;//I2C START action

for(delay=0;delay<10000;delay++);

i2c_send_byte(0x3a);//ACK=ok, i tested it

i2c_send_byte(0x0d);//ACK=ok, i tested it

I2C0_C1 |= I2C_C1_RSTA_MASK;//restart

i2c_send_byte(0x3b); //ACK=ok, i tested it

I2C0_C1 &= ~I2C_C1_TX_MASK; //enable i2c receive

if(I2C0_D); //trigger receive in I2C bus, Here Iam just reading the data register. If i miss this step I cannot receive anything

while(1){

if((I2C0_S & I2C_S_TCF_MASK) != I2C_S_TCF_MASK) break;}

while(1){ if((I2C0_S & I2C_S_TCF_MASK)) break;}

for(delay=0;delay<10000;delay++);

I2C0_C1 |= I2C_C1_TXAK_MASK; //generate no ack condition

I2C0_C1 |= I2C_C1_TX_MASK; //enable transmission, by this the next read of data register will not trigger byte reception

c=I2C0_D; //after completion of reception I read out the data register

if(c == 0x2a) GPIOB_PDOR &=~(1 << 18); //I cannot get the proper result

I hope you can breifly help me, how to receive data on i2c bus!

Thank you in advance!

Roth K.

Re: I2C receive problem with KL25Z

BlackNight — Sun, 04 Aug 2013 11:39:13 GMT

Hi Karl,

just a wild shot: there is an issue in the KL25Z around 'repeated start'. I was bumping into this one, and it could be your problem:

KL25Z and I2C: Missing Repeated Start Condition | MCU on Eclipse

I recommend that you check your clock settings/dividers if this is your problem.

In any case, I recommend that you use a logic analyzer to check what is going on the bus.

If you have another FRDM-KL25Z, you could turn it into a low logic analzyer too (Turning the Freedom Board into a Logic Analyzer | MCU on Eclipse).

Altough I'm using Processor Expert, this post with the sources on GitHub might be helpful:

Extended Driver for the MMA8451Q Accelerometer | MCU on Eclipse

I hope this helps.

Re: I2C receive problem with KL25Z

rothkarl — Sun, 04 Aug 2013 12:51:23 GMT

Thank you for your help!

Formerly i've figured out the lack of restart condition in the silicon erata sheet.

I met a strange thing about the MMA8452Q inertia sensor:

The datasheet of the sensor says that the "Who I am" field is factory programmed at 0x2A value.

I decided to use the onboard USB to serial converter, to debug the received value.

Result: The value as "Who I am" sent back as 0x1A data.

After this I was curious about the other register's default values, and I find out that the other values

are read correctly, only the "Who I am" identification data were incorrect.

Thanks to this documentation problem, I spent 2 days without success, and I have modified my code multiple times

because I thought the problem is with me...

Re: I2C receive problem with KL25Z

rothkarl — Sun, 04 Aug 2013 13:37:20 GMT

Sorry, I made the mistake. When I downloaded the datasheet of the 8452 insted of 8451, thats why I wanted to read 0x2a instead of 0x1a.

The documentation correct, sorry!