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USB superspeed peripherals Forum Discussions

HiOm_1802421
Level 5
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50 replies posted 50 questions asked 25 replies posted

Hi,

My customer is testing I2C master operation using CYUSB3KIT-003.

They used the CyU3PI2cSetConfig() API to set the I2C clock to 400khz.

But the actual frequency measured was 390khz.

Why is it slower than the setting?

How can they get the actual speed to 400khz?

 

Regards,

Hidekazu Omoi

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1 Solution
Hemanth
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First like given First question asked 750 replies posted

Hi Hidekazu-san,

The curving depends on pull-up resistor value and the bus capacitance. If the resistor value is decreased the rise time will be reduced.

The frequency drop could be due to the gpio header used. Please test the frequency isolating external connection to explorer kit by accessing the on board i2c eeprom. Verify if you are seeing 400KHz.

Regards,

Hemanth

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Hemanth
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Hi Hidekazu Omoi,

We tested the frequency on the explorer kit by configuring to 400000 bit rate. we accessed on-board eeprom to check the clock frequency. Frequency observed is 400kHz.

Please see attached image.

Regards,

Hemanth
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Hi Hemanth-san,

I got an I2C measurement waveform from a customer.

According to this waveform, the rise of SCL seems to be rounded.

The device they want to control is connected to the GPIO header.

Is this the cause of the frequency drop?

If correct, do they need to change the resistance to a smaller one to allow more current to flow?

scope_10.png

 

Regards,

Hidekazu Omoi

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Hemanth
Moderator
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Moderator
First like given First question asked 750 replies posted

Hi Hidekazu-san,

The curving depends on pull-up resistor value and the bus capacitance. If the resistor value is decreased the rise time will be reduced.

The frequency drop could be due to the gpio header used. Please test the frequency isolating external connection to explorer kit by accessing the on board i2c eeprom. Verify if you are seeing 400KHz.

Regards,

Hemanth
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Hi Hemanth-san,

I understand.

They may temporarily increase the clock frequency and continue to check the operation, but they will try it later.

Thank you for your answer.

Regards,

Hidekazu Omoi

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