SPI.transfer() will not continue transmitting in void loop

Projects Programming
1

I have tried using this DigitalPotControl example to get SPI up and running on my Uno. I hooked up my Oscilloscope to verify clock and MOSI, but SPI only transmits once.

Am I missing something? I tried the sample code on that example, which implied that multiple transmits should be taking place, but that just is not the case.

I tried to look up documentation on how SPI.transfer should work, but I'm blown away at how poor the documentation is. It seems most of Arduino function details are shared by "word of mouth" on the forums.

2

Please post your code (in code tags, obviously) and your schematic.

No, you have all the detail you could possibly want, installed on your computer.

3

Your post was MOVED to its current location as it is more suitable

4

I copied that code, compiled it and uploaded to my Uno. It looks to transmit once every ~210mS, not once.

5

The code is in the example I linked above.

  • William L.
6

Thanks for confirming Blackfin. I have Channel 1 (Orange) connected to pin 11 for MOSI and Channel 2 (Purple) connected to pin 13 for Clk. In the oscilloscope image I show here, this is the only data that appears after I compile and upload to the Uno. I don't see any repetition of SPI activity after what is shown here, and oddly enough the MOSI data does not seem to change if I modify the value I am sending over the SPI bus, unless I set it to 0.

Blackfin, did you also confirm the timing with an oscilloscope?

Arduino_Uno_SPI
Arduino_Uno_SPI1149×783 36.7 KB

7

Sometimes noobs make transcription errors.

8

Thank you for your continued toxic support. Does a transcription error occur when you ctrl+c and ctrl+v? If you have nothing useful to add, then why even bother trolling the forums for people who are asking for honest help?

9

Not normally, no.
But then people fiddle around with code, introducing the odd semicolon here, or a stray comma there, and don't understand their significance.

10

Welcome to my ignore list.

11

Is there something I did wrong? First "TheMember..." and now you have come in with some negative comments. Is the forum not a place for users to ask questions when they hit roadblocks?

12

We go for the obvious / most likely first, as a form of triage.
First-time posters often make a lot of very basic errors.

Edit: Got to some hardware, and my 'scope.
Yup, it repeats, as expected. (Don't have a digital pot to hand, sorry)

13

Can you zoom out to 50mS/div and check there?

I see this up close:

When I zoom out I see these repeating every 210mS (give or take).

14

1ksps??!!

What do you expect to see at 1ksps when observing a clock that runs at 4MHz and a MOSI signal that will typically change at about that same 4MHz rate? (or for that matter, something that repeats every 210ms?)