Content originally posted in LPCWare by joebobku on Thu Jul 28 13:33:04 MST 2011
Answered my own question.. but for those of you with the same question
[B]Getting debug access to target chip[/B]
It is possible to download an image into the flash on the target that will then prevent further debug connections. The classic cases of this are
[LIST]
[*]The image contains code that sets the MCU clocks up "incorrectly".
[*]The image contains code that enables a watchdog timer.
[*]The image contains code that "switches off" some, or all of the multiplexed debug pins (JTAG/SWD).
[/LIST]
If you do this, then there are a couple of possible ways to try to recover debug access to the MCU (depending upon the MCU being used).
Once you have managed to recover debug access to the MCU, the first thing that you should do is overwrite the image in flash with one that sets the system up in a safe manner, so that future debug connections will be successful without the need to recover debug access again. You would normally use the in-built flash programmer to erase the flash.
[B]NXP LPCxxxx ISP[/B]
The first thing to try with NXP LPC MCU's to recover debug access is to boot into the ISP bootloader. That is, GND the ISP pin, assert RST, then remove the GND to ISP pin. Once in the ISP bootloader, the target clock configuration is stable, and the debug pins are in their default state - you should be able to connect.
[B]Note[/B]: The ISP pin is:
[LIST]
[*]P0.1 - for LPC11xx and LPC13xx
[*]P2.10 - for LPC17xx
[*]For other MCU's, please check the user manual.
[/LIST]
[B]Note for RDB1768 users[/B]
The LPC1768 on the RDB1768 board can be placed into ISP by
[LIST]
[*]Press and hold the ISP button
[*]Press and release the RST button
[*]Release the ISP button
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