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I2C Speed and Frequency

I2C bus specification describes four operating speed categories for bidirectional data transmission:

Standard-mode (Sm)

a bit rate up to 100 kbit/s

Fast-mode (Fm)

a bit rate up to 400 kbit/s

Fast-mode Plus (Fm+)

a bit rate up to 1 Mbit/s

High-speed mode (Hs)

a bit rate up to 3.4 Mbit/s

One more speed category, Ultra-fast mode (UFm), stands for unidirectional data transmission up to 5 Mbit/s.

Configuring the I2C master interface, you can specify the frequency value by calling the DlnI2cMasterSetFrequency() function.

The range of supported frequency values depends on the DLN adapter:

  • DLN-1 and DLN-2 adapters support frequency from 1kHz up to 4MHz.

  • DLN-4 adapters support frequency from 1.47kHz up to 1MHz.

The quality of I2C lines, the values of pull-up resistors and the number of slaves connected to the I2C bus may influence the working frequency of the I2C bus. Besides, the frequency reflects the speed of a single byte transmission, but not the speed of transmitting all data. It is a fact that the time of data processing can exceed significantly the time of data transmission. That is why data transmitted at high speed can have no effect on the speed of the I2C bus if delays between bytes are longer than the bytes themselves.

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