topic Re: JTAG not working when oscilloscope is connected to CLK0 in LPC Microcontrollers

JTAG not working when oscilloscope is connected to CLK0

aurimaspaulausk — Sun, 24 Jul 2016 15:53:22 GMT

I'm using LPC4337with J-link debuger in IAR ide. I noticed that when i connect oscilloscope to the CLK0 pin i'm not able to download the software into CPU and debug, I also see the square signal on CLK0 pin during connection. It seems that CLK0 is internally routed to JTAG pins. Why this is happening? The oscolloscope is 1Mohm 15pF.

Re: JTAG not working when oscilloscope is connected to CLK0

Carlos_Mendoza — Tue, 26 Jul 2016 16:56:28 GMT

Hi Aurimas,

Are you using a NXP evaluation board? Could you tell us the complete part number being used?

Thanks in advance!

Best Regards,

Carlos Mendoza

Technical Support Engineer

Re: JTAG not working when oscilloscope is connected to CLK0

aurimaspaulausk — Thu, 28 Jul 2016 14:22:32 GMT

Hello,

I'm using non NXP manufactured board. It is from Waveshare. Here is the link to the board: http://www.waveshare.com/open4337-c-package-a.htm

I noticed that it is enough to touche the CLK0 pin with the finger and the debug is not working.

I guess CLK0 is connected internally to some circuitry. Because i see signals during the debug on CLK0 pin.

Re: JTAG not working when oscilloscope is connected to CLK0

bernhardfink — Wed, 03 Aug 2016 09:57:50 GMT

Hi,

this sounds weird. The CLK0 pin normally outputs a clock to the SDRAM, on this board it is used as clock output for the SD-card. But after reset it is configured for EMC_CLK0 function.

The pin 45 of CLK0 is not close to the JTAG pins, so a connection between these pins could only be caused by an external shortcut. Maybe test with an ohm-meter for shortcust between CLK0 and other pins, especially the ones from JTAG.

Regards,

NXP Support Team