Author Topic: A simple "JTAG-HAT" board for the Arduino Mega  (Read 2325 times)

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Offline THDplusN_bad

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A simple "JTAG-HAT" board for the Arduino Mega
« on: February 07, 2018, 11:46:39 pm »
Good Day my fellow Arduino enthusiasts,

Prologue:
I frankly admit it: I am late to the Arduino party. However, I became intrigued by the idea of a low-cost, fairly powerful µC-platform over the past years. An opportunity to get me back into programming - I was into VHDL and Motorola HC11-programming many, many moons ago- I am sure some of you will remember those days of expensive tools such as Codewarrior or IAR workbench and endless evenings dealing with mnemonics such as LDAA, LRSA etc...

I am still at the very beginning, but it quickly became obvious that the Arduino "IDE" is nothing but a programming tool - not a real development environment. Support for any level of debugging, stepping commands, monitoring registers - nada.
 
I was then glad to hear about the free ATMEL Visual Studio IDE - only to find out that a) The Arduino Mega2560 µC does not support the so-called debug-wire interface, but JTAG and b) I need an in-circuit-emulator/JTAG device. So, I have placed an order at digikey and a few days later I became the proud owner of an inexpensive Atmel ICE board (again, in comparison to the prices 15..20 years ago!)
I went for the basic kit, which comes with a 10-pin/6-pin cable and USB-micro cable...

- Only to find out that microchip sells the full kit (which includes all common cables and an adapter) at a 50% discount until Feb 28th! See https://www.microchipdirect.com/product/search/all/ATATMEL-ICE (no affiliation with the company) -

The "JTAG-HAT" for the Arduino Mega:
  • The task was to find a convenient way to connect the ATMEL ICE to my Arduino Mega-clone board HW for debugging via JTAG. Again, I am very new to the Arduino universe, but I think the the following little board would be called a "JTAG HAT".
  • What is it?
    A simple HAT board for the Arduino Mega, which connects to the ATMEL-ICE via JTAG and maintains access to all headers /signals.
  • How was it made?
    Main components are a simple, single-sided perf.-board and a 0.05"-pitch cable with 10-pin header (digikey order number is SAM8221-ND at 5.37€ plus VAT).
    I had some 25-pin sub-D connectors in my stock, and decided to use what I had available...
  • Any hints?
    Yes, the following might be useful for others: The trick is to use standard 0.1" female headers and stack them on top of the board connectors in such a way that the resulting mechanical offset affects all connectors same way.
    If you cut-off the connectors for the digital signals of the Arduino Mega a bit, the height can be made to match.
    As a result, the "JTAG-HAT" can be used in conjunction with any other Arduino peripherals as long as the Arduino Mega 2560's port F signals which are also used for JTAG are not used (A4 to A7).
    The Sub-D connector is designed for 0.1" flat cable. I have used some double-sided adhesive tape and precision tweezers to position the 0.05" pitch cable before crimping. See photos for details. A 2nd layer of adhesive tape and a few drops of hot glue were used to re-inforce the mechanical connection. See photos.
     
  • Schematics?
    Sorry, no. I have decided to skip schematics as the design is so very simple. I have added a green LED for the VCC supply, and a simple JFET-based buffer (BF245A) to drive a yellow LED to monitor the JTAG TDI signal.
    All other connections are just 1:1 feed-through.
I was glad to see that after I had set the infamous JTAGEN-fuse on the Arduino Mega using the ISP interface, Atmel Studio 7 reliably connects to the Arduino Mega via my JTAG HAT-board.
It works! :) That will keep me entertained for sure for some time ...

I trust this simple board might inspire others. It took me about 1.5 hrs to build it and 30 min for the design and collecting the needed components.

Cheers,

THDplusN_bad
 

Offline westfw

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Re: A simple "JTAG-HAT" board for the Arduino Mega
« Reply #1 on: February 08, 2018, 02:30:24 am »
I did this a while ago.  Simpler and less flexible, I guess...

https://oshpark.com/shared_projects/HtnXf6wb
 

Offline THDplusN_bad

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Re: A simple "JTAG-HAT" board for the Arduino Mega
« Reply #2 on: February 08, 2018, 07:58:56 am »
Good Day,

westfw, that's a nice PCB, I must say. Thanks.

However, the point was to maintain access to all ports/pins. One can add any other board for the Arduino Mega on top of my board.

Cheers,

THDplusN_bad
 

Online donotdespisethesnake

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Re: A simple "JTAG-HAT" board for the Arduino Mega
« Reply #3 on: February 08, 2018, 08:52:22 am »

It works! :) That will keep me entertained for sure for some time ...

I trust this simple board might inspire others. It took me about 1.5 hrs to build it and 30 min for the design and collecting the needed components.


Nice work!

If I create an equivalent KiCad design, would you help reviewing it?

I did a quick schematic ...
« Last Edit: February 08, 2018, 11:28:12 am by donotdespisethesnake »
Bob
"All you said is just a bunch of opinions."
 

Offline THDplusN_bad

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Re: A simple "JTAG-HAT" board for the Arduino Mega
« Reply #4 on: February 08, 2018, 01:44:00 pm »
Good Day,

sure, see my PM. Thanks!

THDplusN_bad
 

Online donotdespisethesnake

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Re: A simple "JTAG-HAT" board for the Arduino Mega
« Reply #5 on: February 10, 2018, 01:37:12 pm »
With THDplusN_bad I have created a KiCad project https://github.com/bobc/jtag_shield

I also created a sample PCB layout, requires further work.
Bob
"All you said is just a bunch of opinions."
 


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