I2C bus pull up issues after attaching an existing board

[tom_hanks]

Hi there,
I am attaching a existing board on my new design...

on New design I have given Pullup to I2C bus (10K) for 3 devices...
it worked fine....

but after attaching the existing board, I2C bus is not working...

Existing board contains two I2C device with individual pull-up(10K) and 100pf grouding on the SDA/SCL signal......

Can any one see, why it is not working....


Can I use the series termination ?

 

[namqn]

i2c pull up

From the I2C spec., just one pull-up on each wire for the whole bus. Also, remove the caps to reduce the load capacitance of the bus.

Cheers,

 

[tom_hanks]

pull-up sur i²c

thanks..
i did the same...
but still not getting the acknoledge signal from the adressed device....

 

[Davood Amerion]

i2c pull

What is the frequency of I2c bus? some of I2C devices do not work in high frequency, say 100KHz.
another one; Is your source program OK in other situation?

regards
davood.

 

[tom_hanks]

i2c less than 100khz

it is working on 32.76KHz....

I have modified the Src code...to configure the existing board with new design...

xxx

 

[alzomor]

Re: I2C pull up...

Hi

This to conclude the recomendations

1-Short pathes between I2C driver and slaves
2-Single pull up for each of SCL & SDA "don't put pull up for each device"
3-Try to make SDA & SCL tracks identical AS possible
4-Start with very low SCL frequency you can even work at frequency less than 100KHz
5-Make sure that you put the correct Device Address and addess select is correctly configured "if your chip have address select"
6-Finally you can use PC controlled I2C driver for debugging
7-for more details you can check the I2C specs

Salam
Hossam Alzomor
www.i-g.org

 

[mubeen630]

Re: I2C pull up...

Hello,
1. Check to see if voltage levels are same on new devices
2. Can you get some scope plots to see where the problem is, if signal integrity is not compromised
when 2 more devices are placed.
3. Check to see if out of those 2 non working which one is causing a problem.
4. Place 22 ohm terminating resistors.
5. Can also change the pull up values keep it above 4K.
5. It would better if you can hook up a logic analyzer and trigger when you power up.
Regards,

 

[tom_hanks]

Re: I2C pull up...

thank you for all this points....


now there is one pull up of 10K and series resistor of 100ohms....

i am working on 32.76Khz...
but the signal are transmitting higher then 32.76Khz....
around 50Khz.....

may lots of oscilation is going on........

 

[sci-3d]

Re: I2C pull up...

I have an exameple

https://mcu-programming.blogspot.com/2006/09/ic-bus-interfacing.html