topic Strange problem with i2c master on FRDM board in Kinetis Microcontrollers

Strange problem with i2c master on FRDM board

steve_fae — Wed, 06 Mar 2013 04:40:11 GMT

Trying to see any Master i2c bus activity on the FRDM board. I actually turned on both i2c ports [just to make sure something didn't happen to one port.

For one port, I used the I2C_LDD method, basically copied straight out of the "typical usage"

And not seeing any activity on either the clock line or data line [which has a 10K pullup resistor to 3v of course]

I used the higher level component just to send one byte on the other i2c port. .

test: I2C2_SendChar(0xaa);

goto test;

Problem: I don't see any activity at all. The clock lines are non-active. Any ideas?

Re: Strange problem with i2c master on FRDM board

BlackNight — Wed, 06 Mar 2013 07:27:52 GMT

It is possible to cut off the clock from many peripherals on the KL25Z, known as 'clock gating'. But by default this should not be the case.

I suggest that you try one of my examples (e.g. Accelerometer demo) on GitHub if they work for you.

Re: Strange problem with i2c master on FRDM board

steve_fae — Wed, 06 Mar 2013 16:53:04 GMT

Hey Erich, I ran your project and probed the signals at the pullup resistors on the FRDM board. I see activity. When I try to reconfigure the component and move the signals to any other i2c port pins and add some additional 5K pullups I still don't see any activity.

There is a bit of a mystery to i2c on this lovely FRDM board.

Re: Strange problem with i2c master on FRDM board

steve_fae — Thu, 07 Mar 2013 21:24:15 GMT

Got i2c working on the FRDM board. Thanks for your help again Erich.

Re: Strange problem with i2c master on FRDM board

Smiffytech — Thu, 07 Mar 2013 21:52:48 GMT

Just out of interest, what was your solution?

Re: Strange problem with i2c master on FRDM board

steve_fae — Thu, 07 Mar 2013 22:18:52 GMT

Well I still don't have i2c fully running but I now have a clock active during Master i2c transmission. Since I am new to Kinetis programming, I was calling the i2c master transmit from a timer interrupt routine. Basically I am just data logging for time on. When I moved the call outside of the interrupt routine I am now able to see the clock. Interesting to note also is for the eeprom, Microchip only suggests using a pullup on the SDA line. But for the FRDM board, while communicating with the accelerometer, they use a pullup on both the SDA and SCL lines. So I added the additional pullup as well.

Re: Strange problem with i2c master on FRDM board

Smiffytech — Thu, 07 Mar 2013 23:12:53 GMT

Weird about the pull-up on SDA only, unless there is some sort of pull-up in the Microchip part - because the electrical nature of I2C means it HAS to have pull-up resistors on both SDA and SCL. So, if you're doing I2C on pins other than the ones with the pull-ups on the Freedom board, yes, you need those resistors.