JTAG Connection Issues

Discussion created by lpcware Employee on Jun 15, 2016
Latest reply on Jun 15, 2016 by lpcware
Content originally posted in LPCWare by birdbren on Tue Jun 10 06:59:08 MST 2014
We have a prototype development board using the NCP4357 (the 208 pin QFP version) and I have been trying to get it up an running for a week now. The problem is that I can't even get a JTAG to connect properly. It is partially working, since I can see both the M4 and M0 processor ID's on the JTAG chain when I configure the JTAG but as soon as I try to connect, I get errors. Usually the error is that the processor could not be Halted, but someimes it is "Too many devices in the scan chain"

I have tried using both KEIL and their Ulink-ME and the LPC-LINK2 with LPCXpresso as well as a FTDI based Jtag using OpenOCD and they all have similar responses.

Getting details from Keil or LPCXpresso on the JTAG responses is difficult but from OpenOCD I can get a bit more information, and I have been checking the JTAG signals on a scope to confirm. What seesm to be happening is that the JTAG resets properly and starts shifting the Device ID, during this time the JTAG TDI  pin (the input to the JTAG Scan Chain on the 4357) goes High (after the reset and before the data shift starts), the device ID appears on the JTAG TDO pin, but after the 2 32 bit ID's, the TDO pin stays low, even though there are another 14 to 30 registers worth of clocks.

My understanding is that after the 2 Device ID's (64 clocks) the data that I get on TDO should be what was on TDI 64 clocks ago, so I should be getting a stream of 1's after the second device ID, not 0's.

We did check that the DBGEN pin is configured properly to enable the JTAG (changing it gets a different device ID, only 1 32 bit value, but still followed by 0's.

It looks as if the TDI pin is not working - we are currently building up a board with only the CPU and JTAG but I was hoping you may be able to find someone to help.