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CC2500 max tx-sense rate

SAM OAH
Prodigy 210 points
Other Parts Discussed in Thread: CC2500

Hi

I have a question regarding how many times I can do the following operation in one second.

The operation consists of checking the rssi of a channel and transmitting that rssi value and the process goes forever, assuming I am using a 26 Mhz crystal how many times I can repeat this process in a second ?

So far I found that it takes 22 micro seconds to switch from tx to rx and about 10 micro-seconds to switch from rx to tx, 

rssi_update_rate= 2*BW_channel / (8*2^filter length)

Assuming i am using the default filter length of 16 and the channel B.W is 812 Khz it results in approximately an update rate of 10^5 per second i.e., 10 micro seconds so can I just add up those number i.e., saying

sensing: 10 micro-seconds

switch from Rx-> Tx=22 micro-seconds

Tx time = ? (how much is this time)

Switch back to Rx=10 micro-seconds

------------------> Repeat the process gain-------------------

is that approach correct? if not, can you point out which times I am mising out 

  • 0
    TI__Guru 56590 points

    Hello Sam,

    I calculated the update rate to be 3 times per seconds (333.3 ms refresh rate) for the configuration you describe. You should decrease the filter length to reduce the refresh rate of the RSSI register further.

    -->(2*812e3)/(8*(2^16))
    ans =
    3.0975342

    You must also consider the PLL calibration time of 721 us. If the temperature is stable you can calibrating each frequency at start-up and saving the resulting FSCAL3, FSCAL2 and FSCAL1 register values in MCU memory and when changing the frequency, the calibration process can then be replaced by writing the FSCAL3, FSCAL2 and FSCAL1 register values corresponding to the next RF frequency. Or else you will need to run the calibration each time.

     

  • 0 in reply to Eirik V
    Prodigy 210 points

    Hi Eirik

    Thank you for your response and sorry for my late verification of the answer (I thought I verified it earlier).

    So basically what I am understanding from u is that:

    I have to wait 333 ms (or around that time before taking the next RSSI reading?)

    So lets say I am using the span of 58 Khz and I am building a spectrum analyzer using the CC2500, I have to scan the current 58 khz, jump to the next one (go IDLE and change the channel frequency or the channel ID, then go back in RX mode again) then wait for 333 ms and do the RSSI reading for the current 58 khz ?

    Is it so? or I am missing something.

    Your help on this issue will be much appreciated.

    Thank you again.

    Sam.