NRF52840 JTAG issue

[Dilrosh]

Hi,

From last couple of months I'm working on NRF52840 chip and designed a battery operated device. I also made 5 prototype boards and I'm happy with the range test, coded PHY etc.. But right now I'm unable to reflash my 3 chips (out of 5 boards) but the old code flashed in the chips are still working. In short my all 5 boards are working but in 3 boards I'm not able to reflash the chips.

Hardware check done

• All connections are rechecked and it is fine
• All the internal voltages are coming properly
• Oscillators are working properly

Queries

• Is there any protected mode for NRF52840 so that no of them can reflash the chips?

Please find the serial window, these are the messages I got while connecting my JTAG to my device.

Regards,

Dilrosh P S

[Vidar Berg]

Hi Dilrosh,

Have you checked the VDD voltage on the failing boards? VDD defaults to 1.8 after a full chip erase if you use high voltage mode (REG0), and not all programmers support that. 

Is there any protected mode for NRF52840 so that no of them can reflash the chips?

 Yes, but the jlink commander log will usually indicate that the chip has been locked. Anyway, I suggest that you try nrjprog and run nrfjprog --recover to make sure. This will disable readback protection if it's enabled.  

Regards,

Vidar