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CC1200: RFStudio Register Differences between Packet TX/RX

Karun Koppula
Prodigy 100 points
Part Number: CC1200

I've been working with a CC1200 DK to better understand the use of the chip and found that I'm seeing some difference in registers between Packet TX Mode and Packet RX Mode for the same set of RF Parameters. While working with the CC1200 on a proprietary board, I have found that TX range seems to be much shorter than expected and was wondering if this could be related.

RF Parameters

  • Carrier Frequency: 903-927 MHz
  • Xtal Frequency: 40 MHz
  • Symbol Rate: 500 ksps
  • Bit Rate: 500 kbps
  • RX Filter BW: 833.33 kHz
  • Modulation Format: 2-FSK
  • Deviation: 124.816895 kHz
  • TX Power: 14 dBm
  • PA Ramping: Enabled
  • Whitening: Enabled
  • Performance Mode: High Performance
  • Image Compensation: Enabled

The rest of the register values are as given by RFStudio.

Between Packet TX Mode and Packet RX Mode there are a few differences.

CC1200 Registers Packet TX Mode Packet RX Mode
FS_DIG1 0x04 0x07
FS_DIG0 0x50 0xAB
FS_DVC1 0xF7 0xFF
FS_DVC0 0x0F 0x17

From the register descriptions in the user manual and from SmartRF Studio it seems that many of the bits involved are supposed to be sourced from SmartRF studio. Do these values need to be explicitly written to the chip in the different modes?

  • 0
    Prodigy 100 points

    Would you also be able to clarify which registers a frequency calibration strobe affects? It's not entirely clear to me which registers need to be set when using different frequencies. It appears that writing the new center frequency and calling the cal command is sufficient for using another channel. Should all of the registers on the chip be explicitly written with the values from SmartRF Studio or just those shown in green on SmartRF Studio?

  • +1 in reply to Karun Koppula
    TI__Guru**** 317180 points

    All registers that are given by SmartRF Studio that are different from the reset value have to be written to the chip.

    The FS_x registers have to be set according to SmartRF Studio to set the synth settings to get optimal performance. The settings are set differently in RX and TX to give the most optimal phase noise etc.

    To use a different channel, write a new frequency to the FREQ registers and do a SCAL.  

  • 0 in reply to TER
    Prodigy 100 points

    To be explicitly clear, the FS_x registers need to be written with the appropriate values for every transition to TX or RX modes. Is that correct?

  • 0 in reply to Karun Koppula
    TI__Guru**** 317180 points

    - All FS_x registers that are different from the reset value has to be written to CC1200 at start-up

    - When switching to/ From RX/ TX you have to write the FS_x registers that are different between RX and TX.