TM320F28335 and XINTF: approximately 1/2 volt 150MHz sawtooth waveform riding on XINTF write strobe line

stevenh

Guru 20035 points

I am debugging an issue where the XINTF write strobe line doesn't go low during a write. I am using the Example_2833xDMA_xintf_to_ram example in control suite.

I noticed that after I execute the XintfRegs.XINTCNF2.bit.CLKMODE = 0; line in init_zone7(), an approximately 1/2V 150MHz sawtooth waveform appears on the write strobe line. I haven't taken the time to notice if this waveform is also appearing on the other XINTF lines.

Below are oscilloscope snapshots showing before and after executing the XintfRegs.XINTCNF2.bit.CLKMODE = 0; line.

What would be the reason for the waveform appearing on the write strobe line?

Update: this waveform is also appearing on the other XINTF lines.

Stephen

over 9 years ago

0 stevenh over 9 years ago

Guru 20035 points

Hello,

Stetting XCLKOUT mode off (i.e. XintfRegs.XINTCNF2.bit.CLKOFF = 1;) gets rid of the sawtooth waveform.

Does this mean there's an issue with the board?

Stephen

0 Vivek Singh over 9 years ago in reply to stevenh

TI__Guru** 113655 points

Stephen,

How is this XCLKOUT signal used on board? You also mentioned in update that it's impacting other XINTF signals as well. Which all signals are getting impacted due to XCLKOUT?

Regards,

Vivek Singh

0 stevenh over 9 years ago in reply to Vivek Singh

Guru 20035 points

Hello Vivek,

"How is this XCLKOUT signal used on board?"
Its not used for anything right now.

The sawtooth waveform is showing up on all the XINTF lines, however, its showing up on some lines more than others. XWE0n seems to be the worse.

Stephen

0 Vivek Singh over 9 years ago in reply to stevenh

TI__Guru** 113655 points

Hi Stephen, Is this issue resolved?

Regards,
Vivek Singh

0 stevenh over 9 years ago in reply to Vivek Singh

Guru 20035 points

Hello Vivek,

The last time I checked the sawtooth waveform was still there. It only happens when I enable XCLKOUT. Do you think this is a PCB issue?

Stephen

0 David M. Alter over 9 years ago in reply to stevenh

TI__Guru 61235 points

Stephen,

XCLKOUT pin is basically acting as an antenna and transmitting the XCLKOUT signal into your board. This is getting picked up by other traces. Just turn off the XCLKOUT signal. Problem solved, yes?

Regards,
David

0 stevenh over 9 years ago in reply to David M. Alter

Guru 20035 points

That's what I expected.

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TM320F28335 and XINTF: approximately 1/2 volt 150MHz sawtooth waveform riding on XINTF write strobe line