Connecting to LPC2138 w/ J-Link ARM Solution

doerity · February 8, 2010 at 6:49 PM

I have been having problems using a J-Link ARM and connecting to a LPC2138 on custom hardware. See previous post ([ANSWERED]Connecting to LPC2138 w/ J-Link ARM Pro) for details. However I have found the solution to this problem. The LPC2138 JTAG pins can be multiplexed with GPIO pins. After reset the LPC2138 will sample the RTCK pin and if this is low the JTAG pins will be used as JTAG, otherwise they will be used as GPIO pins. I'm not sure if the reset strategy in software can account for this by bring RTCK low while releasing the device from reset of if there needs to be documentation added that a pull down is needed for this pin.

SEGGER - Rolf · February 21, 2010 at 11:56 AM

Thanks for providing the solution to the problem.
You are right, the chip samples RTCK after Reset and it requires a pull-down.
This may indeed be a problem for many people designing their own hardware, but it is
clearly written in the NXP manual.
May be worth considering to copy it to the J-Link manual under "device spcifics", but I do not
think we really want to do so.
We expect customers to either read the chips manual or simply copy the relevant parts
of the schematic of the eval board when designing your own hardware.

So, in general the procedure we recommend we doing a new design:

a) Get an eval board with the device
b) Test J-Link and your tool chain with the eval board. There should not be any problems. If there are, get in touch with
the tool provider (be it Segger for the J-Link or anybody else for the compiler/debugger)
c) Design your own hardware. Schematics should be close to the schematic of the eval board.
d) Test your custom hardware. If it does not work like the eval board, look for differences.

Again, thanks for proving the answer.

Connecting to LPC2138 w/ J-Link ARM Solution

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