MSP430FR2433: question about timer capture Mode

Ghilain Pujol

Part Number: MSP430FR2433

Hi,

I am using the MSP430FR2433 in my application, in order to measure the frequency of squares, between 100Hz and 2MHz (a quite big range). I found out this page on TI Resource Explorer, where it is explained how to do this application :
Timer - Capture Mode

On this page, a tutorial is given about how to obtain the value of a 5kHz square wave frequency. I tried this code for my application and it was functional for low frequency applications. but when the signal I use at the input is over 25kHz of frequency, the captured value "signalFreq" is blocked at 25kHz.

Can you help me figuring out how to deal with it, and/or give me some advices ?

Thank you by advance !

Regards,

Ghilain

over 3 years ago

+1 Bruce McKenney over 3 years ago

Guru 100785 points

You will not succeed in measuring 2MHz using capture. My usual estimate is that you might be able to capture 50kHz (with a few heroics), but you won't have time to do much else. At 2MHz, even with a 16MHz CPU, you have only 8 CPU clocks per capture, which isn't even enough to detect the capture and read the result.

To measure a high-frequency signal you should connect the signal to (e.g.) TA0CLK and use the counter to count pulses. By sampling the counter (TA0R) periodically, you can use that result to compute the frequency. Your CPU needs to run at least as fast as the (fastest) signal -- I suggest 8MHz.

This frequency-counting method isn't ideal for low-frequency signals, since the long latencies risk loss of precision (lots of 0s), but it can be done.

This thread shows a simple example of frequency counting. It's for a different device, but the principle is there:

https://e2e.ti.com/support/microcontrollers/msp-low-power-microcontrollers-group/msp430/f/msp-low-power-microcontroller-forum/1067764/msp430fr2355-frequency-counter/3967541

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MSP430FR2433: question about timer capture Mode