JTAG connection dead

Discussion created by lpcware Employee on Jun 15, 2016
Latest reply on Jun 15, 2016 by lpcware
Content originally posted in LPCWare by tecow on Sun Feb 14 13:37:52 MST 2016
Hi, I am using a hardware with the LPC4370 + a 4MByte external SPI flash.

Without any obvious reason the JTAG connection stoppded working after month of proper operation (now I am using lpcxpresso 8.0)
Sometimes things happen with EMC noise etc. and so I took a 2nd board and again after a week of proper operation,
JTAG is again dead - this make me believe it is not EMC.

I measure the JTAG signals after initiating a flash sequence (IspReset) and saw the following strange signals:

Pin 2 (SWDIO) starts with 2.8V and went after starting the transfer to 1.5V ???? (Is the processor driving SWDIO after Reset?)
Pin 4 (TCK) 10 kHz clock on TCK (Pin 4)
Pin 6 (TDO) stays at 3.3V
Pin 7 (a nice low pulse for 5ms) after switched to lpcxpresso 8.

I don't think it is a issue with my JTAG configuration. It works with another board and also with the LPC-Link as Debug Target.
I am just wondering if I really damaged 2 boards or is there any possiblity how the JTAG interface can be brought statically into
such a state (CRP prog, by chance?) Do you see any way to re-enable JTAG?