JTAG dead. Core ID 0xFFFFFFFF is ther a fix?

Development Boards MicroMod
1

For some reason, my JTAG quit communicating. LPC2148. JLink.exe says “Could not find a device on JTAG chain”. I am not getting a correct core ID. Another JTAG board works, so it is not the driver, or cable etc.

Is there a way to recover from whatever happened?

Thanks.

2

Is there a pull-down on the RTCK pin? (P1.26, or pin 24)

Without the pull-down on RTCK, the JTAG interface is disabled and the JTAG pins default to GPIO.

3

Yes, there is a 10K pulldown. On my board it is a DBG_E jumper enabling the pulldown. It is High with the JTAG cable plugged in though, and goes low when I unplug the JTAG cable.

4

I should have said: it needs a low-level on RTCK during reset.

As far as I know, RTCK is an output for the LPC and an input for the JTAG cable, so the JTAG cable should not cause it to go high. So I don’t know what is happening.

Other stuff to check:

  • Is the bootloader still working? I just read on the LPC2000 mailing list that a corrupted bootloader can result in JTAG no longer working.

  • Did you enable code protection? I remember reading somewhere that JTAG is disabled when code protection is enabled. I think you can clear this by doing a full erase using the Philips ISP utility.

  • In case you’re using a header board, is it still properly seated on its motherboard?

  • Did you try to remove and re-apply power to your board?

5

Thanks! I guess i needed a reset with that pin low, (with the JTAG cable removed). I tried probably every other sequence but that! Looks like it works again.

Thanks