USBDM_SWD_SER_JS16CWJ and 1.8V target power supply

[josérubio]

Hello,

I'm currently developing a small project with a K10 MCU.

I'm supplying the target board where the MCU is located with 1.8V from a buck converter, I'm trying to debug the program with USBDM powering the VDD_BDM pin at JP2 with 1.8V from the target, I thought that with this connection would be enough.

No.

With "ARM Programmer" I can detect the MCU but when I want to erase the flash, programming and of course, debugging, an error appears.

What am I doing wrong?

Thank you very much.

[josérubio]

Pgo,

I've been occupied with other things and up to now I can't resume the work.

I appreciate your answer and I apologize by the delay of my reply.

- The JS16 board works well above 2.2V.

- If I increase the capacitors none changes, the same behaivor occurs.

- The waveform of the power supply if relatively free of electrical noise.

I revised the LV125 datasheet from NXP that I used in the board and voltage opperation is from 1.0V to 5.5V and I think that must works.

Checking the schematics from you (http://usbdm.sourceforge.net/USBDM_V4.11/USBDM_JS16/html/USBDM_SWD_SER_JS16CWJ.pdf ) I note that signal RSTn_I is not pulled up, the other input signals to the JS16 are pulled.

Can this be the origin of the issue as the signal level (at 1.8V) falls under the "1" detection of JS16?

If not... why this signal is not tied to 5V?

Thank you very much for your attention and your tools.

José R.

[pgo]

Hi José ,

The main purpose of the external pull-ups on the other inputs is to improve the rise time.

The reset signal is relatively low frequency so I did not think it necessary.

The JS16 inputs have a internal pull-up but it is much larger than the 1k5 external ones.

This has been adequate so far.

I would not think this an issue but it wouldn't do any harm to try adding an external resistor to RSTn_I to see if it makes any difference,

bye

[josérubio]

I see...

You're right, I checked pulling up RSTn_I and I didn't note any difference, I increased the bypass capacitor with no results.

[pgo]

Hi Jose,

I have not tested the JS16 version at 1.8V which is below the minimum (2V) of the 74LV125a used as the interface.  I would however expect it to still be workable.

Could you check the waveforms at the interface to see if they appear OK?

• Could you confirm the operation at a higher voltage?
• If the problem only occurs during programming could you try increasing the bypass capacitors on power supply.
• Check the waveform on the power supply.

bye

[josérubio]

Please,

Have anyone any idea???