• Locked Locked
  • Replies 3 replies
  • Subscribers 79 subscribers
  • Views 1224 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

how to measure MSP432 ADC14 works in 1MSPS exactly?

bj Wang
Prodigy 235 points

Hello everyone

I am working on a project which needs ADC works in max frequency.

I configure ADC work with DMA.

ADC Setting:

clk: 25M using DCO

mode: repeat-single-channel and automatic  mode

hold time : 8 cycles

conversion time: 16 cycles

DMA setting:

work in PINGPONG MODE, transfer 256 data each time, data length is 16 bits, triggered by ADC14

In the DMA interrupt handler, i will toggle a gpio to measure duration of 2 DMA transfer.

I got the result below. It seems that it takes ADC14 265us to generate 256 samples and not expected 256us.

Any comments to my experiment?

Thank you.

  • Prodigy 235 points

    sorry, missed the picture of test result

  • in reply to bj Wang
    Guru 46710 points

    Hi!

    It seems you are doing everything ok unless you made some unexpected software overhead in the DMA isr. If possible, just show DMA ISR and other code which possibly can interfere with timing of the test. 

    First you shall check that your clock frequency indeed is 25MHz. Route clock to corresponding pin and measure frequency. Then you shall chek that everything about ADC configuration is ok.

  • Guru 58965 points
    Do you have a signal generator that can generate a saw-tooth waveform at 1 MHz with appropriate min/max voltages? If so, and you sample it at "exact" 1 MHz, you will get a constant digital reading. If the sampling frequency is slightly off, the digital readings will change slowly. (At the "beat frequency".)

**Attention** This is a public forum