Forum Discussion

Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
10 years ago

Board signals

Hi,

I'm working with a Cyclone II board from Knjn and suspect something isn't right with some signals coming from the board.

All I'm trying to do is to use the LPM_COUNTER as a frequency divider. Depending on the frequency, the amplitude isn't the same and most importantly the signals do not look square at all.

Could you please have a look at the pic attached and let me know if it seems alright ? It should be a 1.5 MHz square signal. The frequency part looks alright to me however the square part isn't neat.

I've tried it on two different boards, on several pins, with different probes.

I would be very grateful for any help.

Best regards,

Jennifer

2 Replies

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    10 years ago

    Check the ground connection: you get that kind of wave when you have poor ground connection; I mean probe ground not connected or far from measuring point.

    Another guess: are you driving that signal on long lines? If so, that ringing is present on the actual signal and you may need to put some termination to prevent it.

    I see on the display DC full. If you are using a >100MHz oscilloscope, limit its channel bandwidth to 20MHz. No need to use full, since your probe would catch up a lot of noise, although I think this is not an issue here.
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    10 years ago

    Thank you for your help, changing and adjusting the probe did the trick.