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CC1200: Help with Symbol Rate Programming

Alexandre Monk
Prodigy 10 points
Part Number: CC1200

Hi all, the programming guide for CC1200 gives the symbol rate register definitions as shown.

However, the equations don't seem to check out; with the default SRATE_E value of 4 and the default SRATE_M value of 239914, the symbol rate comes out to be:

( (2^20 + 239914) * 2^4 * 40Mhz / 2^39 )ksps = 1500ksps which is well above the allowable limit of 500ksps.

What am I missing? Is the exponent signed or would it just max out at 500ksps or am I misunderstanding the equation?

Thank you for any help!

  • 0
    TI__Genius 11275 points

    Hi,

    The easiest (and most reliable) method for this is to use SmartRF Studio 7 to calculate the required register values:

    SmartRF Studio 7: https://www.ti.com/tool/SMARTRFTM-STUDIO

    You can also refer to Section 5.4 of the CC120x User's Guide for information on symbol rate programming:

    SWRU346 (CC120x Low-Power High Performance Sub-1 GHz RF Transceivers User's Guide): https://www.ti.com/lit/swru346

    I'm not sure where have you got the default value of SRATE_E from. As you will find when looking at the SYMBOL_RATE register values in SmartRF Studio, the SRATE_E value will depend on your desired data rate (so there is no default, per se). For 500 ksps (which is indeed the maximum), the recommended value of SRATE_E is 0x0C.

    Regards,

    Zack