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CC2541 I2C Master Clock Rate Calculation

Rob Oppen
Prodigy 90 points
Other Parts Discussed in Thread: CC2541


The CC254X User's Guide gives example clock rates for an I2C master but doesn't provide a formula for calculating rates outside of the table. Does anyone know how the three clock rate bits in the I2CCFG register affect the clock rates? Here's a copy of Table 20-6 'Clock Rates Defined at 32MHz' in section 20.1.5:

CR2 CR1 CR0 Bit Frequency Clock (kHz) Divided by
0    0   0           123                 256
0    0   1           144                 244
0    1   0           165                 192
0    1   1           197                 160
1    0   0           33                  960
1    0   1           267                 120
1    1   0           533                 60
1    1   1           Reserved            N/A

  • 0
    TI__Mastermind 19350 points

    I don't understand your question - there are no clock rates outside of the table: 2 ^ 3 = 8 ... and all 8 permutations are listed in the table.

  • 0 in reply to Dirty Harry
    Prodigy 90 points

    Dirty Harry said:

    I don't understand your question - there are no clock rates outside of the table: 2 ^ 3 = 8 ... and all 8 permutations are listed in the table.

    You're correct. I guess my confusion was with the fact that they only defined non-standard i2c rates.

    Thank you for your response!

    -Rob

  • 0 in reply to Rob Oppen
    TI__Mastermind 19350 points

    What are the standard I2C rates?

    I would have imagined that there would not be a standard rate becuase it is a synchronous bus (like SPI - how can you define a standard bit rate for SPI?). Obviously, an asynchronous bus like UART has standard rates, like 115.2 kBaud, etc.

  • 0 in reply to Dirty Harry
    Prodigy 90 points

    See the different revisions of i2c here:

    http://en.wikipedia.org/wiki/I%C2%B2C

    Sure, as a master I provide the clock but there are typical rates that are universally used (100-kHz and 400-kHz are the two that come to mind) but not supported by the CC2541.

    Anyways, thank you for your help.

  • 0 in reply to Rob Oppen
    Expert 1160 points

    Hello,

    Sorry for opening this thread after two long years. But I have the same question. If I need 100kHz or 400kHz clock frequency at I2C SCL, how can I configure it in CC2541?

    I'm trying to communicate with accelerometer connected to I2C pins but in debugger, the code always gets stuck in I2C_STRT(); What configuration would prevent this from happening. Can provide more info if necessary.