I2C Waveform not Square

[Ambrose]

Hi,

I am using an RCM3100 to control some devices on an I2C bus. I am
using the default Port D lines with a 100K pull up. When I checked the
waveforms, I found that the SCL and SDA lines were not square, but
rather sawtooth.

I suspected some problem on the PCB, so I disconnected all other
circuitry, but the waveform remains the same. I changed the port type
to normal (not open drain) and I get a perfect square.

Can somebody help?

Thanks in advance.

Ambrose






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[WEBDYN]

100 k is too high value for resistor pull up
,
try 2.2 k or 4.7k

Post by Ambrose
Hi,
I am using an RCM3100 to control some devices on an I2C bus. I am
using the default Port D lines with a 100K pull up. When I checked the
waveforms, I found that the SCL and SDA lines were not square, but
rather sawtooth.
I suspected some problem on the PCB, so I disconnected all other
circuitry, but the waveform remains the same. I changed the port type
to normal (not open drain) and I get a perfect square.
Can somebody help?
Thanks in advance.
Ambrose

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[Ambrose]

Thanks Rene, for your help.

I tried 4K7 and the waveform is much better - almost square!!

Post by WEBDYN
100 k is too high value for resistor pull up
,
try 2.2 k or 4.7k

Post by Ambrose
Hi,
I am using an RCM3100 to control some devices on an I2C bus. I am
using the default Port D lines with a 100K pull up. When I

checked the

Post by WEBDYN

Post by Ambrose
waveforms, I found that the SCL and SDA lines were not square, but
rather sawtooth.
I suspected some problem on the PCB, so I disconnected all other
circuitry, but the waveform remains the same. I changed the port type
to normal (not open drain) and I get a perfect square.
Can somebody help?
Thanks in advance.
Ambrose

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