CC2541 I2C work abnormal

Hello Michael,

1. Are you observing this on the SensorTag or a custom board?
2. What pull-up resistor values are you using?
3. How is the accelerometer connected, is it on the same board as the CC2541?

Thanks,

Hi, Quote,

please refer to the below answer:

1. we have only two sensortag test board, and we don't observe the issue on sensortag.

2. the pull-up resistor values is 2.2K

3. the accelerometer is connected by I2C, and it is the same as the CC2541 reference design.  we don't modify the I2C code.

 Thanks.

Michael

Hello,

1. Check the output of the i2c on an oscilloscope.
2. Do a resistance measurement from the i2c pins to the accelerometer to verify resistance.
3. Check resistance from i2c to VCC and GND.
4. Ensure that your board is properly cleaned and all flux has been removed.

Thanks,

Hi, Greenja

please refer to the below answer:

1.  please refer to the attached files.

2.    VCC-SDA 2.18K

       VCC-SCL 2.18K

3.    VCC-SDA 2.18K

       VCC-SCL 2.18K

       GND-SDA 80K，increase to 400K in　10 second
       GND-SCL 80K, increase to 400K in 10 second

4. we ensure the board is properly cleaned and all flux has been removed.

Thanks.

Hello Michael,

What was the resistance measurment of the SDA and SCL trace lines from the CC2541 pins to the Accelerometer pins?

Is there anything else connected to the i2c other than the accelerometer?

Do all the other things attached to the CC2541 work properly?

You wouldn't be measuring resistance when the board is powered up.  That increase in resistance is a voltage induced one.

You need to do a dual trace comparison with both SCL and SDA.  Both your i2c readings should look as clean as SCL-04.jpg. If both measurements coming from the CC2541 pins look like that and reading from the accelerometer look like the other images then you have some impedance in the traces or your CC2541 is not properly mounted.

Check your design layout and inspect an unpopulated board for any grounding or high trace resistance measurements. If you followed the reference design and used the proper tolerances on the Bias 56.0K resistor, along with the filter capacitors then all measurements should match that of the SensorTag.  If not, then it is time to do a redesign.

Thanks,

Hello Greenja,

please refer to our answer:

What was the resistance measurment of the SDA and SCL trace lines from the CC2541 pins to the Accelerometer pins?

[Michael_20140905]the resistance of the SDA and SCL trace lines from the CC2541 pins to the Accelerometer pins is near 0.1 ohms. It is 6mil width and 20mm length, copper trace. There is no resistance device between accelerometer and CC2541.

Is there anything else connected to the i2c other than the accelerometer?

[Michael_20140905]No. The I2C is only connect to accelerometer.

Do all the other things attached to the CC2541 work properly?

You wouldn't be measuring resistance when the board is powered up.  That increase in resistance is a voltage induced one.

[Michael_20140905]Yes，I measure resistance when power down.

You need to do a dual trace comparison with both SCL and SDA.  Both your i2c readings should look as clean as SCL-04.jpg. If both measurements coming from the CC2541 pins look like that and reading from the accelerometer look like the other images then you have some impedance in the traces or your CC2541 is not properly mounted.

[Michael_20140905]I’m sorry that the oscillograph we used can’t record all the wave of SCL&SDA. The error phenomenon appear random. We test a holl night to re-appear the error phenomenon. So we can’t send the picture you want immediately. 

Check your design layout and inspect an unpopulated board for any grounding or high trace resistance measurements. If you followed the reference design and used the proper tolerances on the Bias 56.0K resistor, along with the filter capacitors then all measurements should match that of the SensorTag.  If not, then it is time to do a redesign.

[Michael_20140905]I don’t find the Bias 56K resistor in the SCH of SensorTag,you can see the SCH of petkit and SensorTag in the attachment.

The Bias resistor is R301 in the schematic.http://www.ti.com/lit/zip/swrr109

Note: You should include the image in your post and not as an attachment.  The file sizes are very large and use up a lot of data which is not good when you are on a data plan.  Put the image in the post and reduce its resolution to webpage dpi.

Thanks,

Hi, Greenja,

Our board has the R301, you can help to review our schematic in the last mail attachment.

thanks.

Hi, Greenja,

Could you give me some idea for I2C issue?

Thanks.

Here are some options:

1. Revove the accerometer and test the CC2541 i2c with another i2c device
2. Make a separate board with just the accelerometer.  Test it with the sensotag.

These two options will pinpoint where your problem is.