Electronic – Consensus on proper wiring for Cortex M 10 Pin JTAG Connector


For the past few weeks I have been working with the new revision of my ARM Cortex M4 design that I posted about a month ago, thanks again to everyone who provided me with much needed guidance and information! Anyways I am still having trouble getting my ARM to program via JTAG programmer. I am using the NXP LPC4337JBD144 ARM Cortex M4, I am using their LPCXpresso IDE and LPC-Link JTAG/Debug module. So far after many attempts I have been unable to get the JTAG interface to recognize my chip as a programmable target.

When creating this new design (the first did not work) I was very careful to check the datasheet and with NXP representatives to make sure that the hardware configuration was absolutely correct before having the board fabricated. My original design suffered from an improperly wired JTAG connector, lack of bypass caps on all voltage inputs, and the lack of jumper pins on crucial JTAG configuration pins. When setting up the JTAG connector circuit I consulted NXP support and the datasheet for the chip. The datasheet instructed me to only have pullups on two of the pins, one NXP rep told me to pull all pins down with 10k ohm resistors, and another told me to pull all pins high with 10k ohm resistors. Around that time I posted here and consulted with friends far more experienced than me, between those sources I decided to pull all pins high with 10k pullups.

Over the weekend I swapped out the chip maybe thinking that I might have damaged the first one but I was still unable to get it to program, so I went through all the datasheet but I could not find a solution when reading through the section on the JTAG interface. My next thought was to look at the evaluation boards made for the same ARM that I am using. I discovered that the boards from Hitex and Keil had unique JTAG connector wiring, both different from what NXP instructed me to do. This discovery has been rather confusing and what I really would like to know is which is the right way to wire it? Is there a standardized wiring scheme meant for all Cortex M ARM based micro?

Here is a schematic document I made illustrating the different configurations as well as the reset circuit and TRST/DBGEN jumper pins.

Best Answer

This is the official ARM Cortex JTAG/SWD connector diagram:

Cortex 10 pin connector

You should follow the data sheet/user manual about any resistors that are required. SWD pins on other LPC chips are usually pulled up internally.

The LPCXpresso IDE might be defaulting to the SWD interface. You need to select the JTAG interface, which is probably what the LPC4337 uses initially.