I2C supported clock speeds

[SkyRyder]

Hi all,

I could not find what clock speeds metro express airlift supports for I2c (via the Wire.setClock() function).

Also, what is the default speed? (usually 100kHz, right?)

Anyone know?

Thank you!

[User_UMjT7KxnxP8YN8]

From wire.h:

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    // TWI clock frequency
    static const uint32_t TWI_CLOCK = 100000;

From wire.cpp:

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void TwoWire::begin(void) {
  //Master Mode
  sercom->initMasterWIRE(TWI_CLOCK);
  sercom->enableWIRE();

  pinPeripheral(_uc_pinSDA, g_APinDescription[_uc_pinSDA].ulPinType);
  pinPeripheral(_uc_pinSCL, g_APinDescription[_uc_pinSCL].ulPinType);
}

[SkyRyder]

If I understand this correctly, the default speed is 100000kHz?

what speeds are "legal" to use that are significantly slower? Is there a document on this that a newbie can understand?

I believe the command Wire.setClock() is how it is set, correct? should it be called before or after Wire.begin?

Thank you.

[User_UMjT7KxnxP8YN8]

It's 100 KHz. I'm just looking at the code, which you can do too. On a Windows PC, it's located at
C:\Users\[YOUR_USERNAME_HERE]\AppData\Local\Arduino15\packages\arduino\hardware\samd\1.8.11\libraries\Wire

From wire.cpp:

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void TwoWire::setClock(uint32_t baudrate) {
  sercom->disableWIRE();
  sercom->initMasterWIRE(baudrate);
  sercom->enableWIRE();
}

Other useful resources include the official Arduino refence page for Wire at https://www.arduino.cc/en/Reference/WireSetClock which says:

Wire.setClock()
Description
This function modifies the clock frequency for I2C communication. I2C slave devices have no minimum working clock frequency, however 100KHz is usually the baseline.

Syntax
Wire.setClock(clockFrequency)

Parameters
clockFrequency: the value (in Hertz) of desired communication clock. Accepted values are 100000 (standard mode) and 400000 (fast mode). Some processors also support 10000 (low speed mode), 1000000 (fast mode plus) and 3400000 (high speed mode). Please refer to the specific processor documentation to make sure the desired mode is supported.

You can find the ATSAMD51 processor family datasheet at https://www.microchip.com/content/dam/m ... 01507G.pdf