Issue 143 June 2002
Still Swimming With the STK500
Onto the JTAG ICE

USING THE JTAG ICE

The JTAG ICE comes with everything you need to get you coding and debugging quickly. Most of the JTAG ICE installation process was a no-brainer. But, the person or machine that assembled the 10-pin JTAG interface ribbon cable had me swinging at a slider. Because the Atmel engineers went to the trouble of color coding the JTAG-to-STK500 development board ribbon cable and meticulously detailing the JTAG ICE JTAG header, it would have been easy to just trust the colors and connect the JTAG ICE to the STK500 development board with the brown lead being pin 1, the red lead pin 2, and so forth.

If this isn’t your first time reading my words in Circuit Cellar, you know that I have an affinity for smoking things. To avoid letting the magic out of the little plastic boxes, I’ve started checking everything and trusting nothing. As it turns out, the ribbon cable was assembled in the reverse order with the brown lead representing pin 10 of the JTAG connector and the black lead posing as pin 1. I scratched my head, gathered my thoughts, hooked the suspect JTAG cable to a VOM, and shot the leads. I wasn’t losing it; the cable was indeed assembled backwards.

I continued on with the installation process and connected the JTAG ribbon cable “backwards” and was able to use the JTAG ICE without melting it. I really don’t think I would have harmed anything if I had not been attentive. It just wouldn’t have worked until I corrected the wiring. That’s really the only problem I had during the JTAG ICE install. I was able to obtain all of the latest firmware and front-end software from the Atmel web site and from there I was off to the races. My AVR development system hardware is shown naked in Photo 3.

I develop with a dual-head monitor system. This allows me to put the ICCAVR application on the right monitor and AVR Studio on the left monitor. The ImageCraft AVR C compiler IDE is excellent. I am able to segregate my code using projects. I created a separate test project to actually code and debug my AVR C code one module or line at a time. In the same ImageCraft IDE window structure, I opened another window of C source that would eventually be the completed working code that would be loaded into the ATmega16. The final working code window code is not included in the test project. I debugged code snippets in the test project and moved the working routines over to the final code window as I finished them. All of the code writing and compilation was performed on the ImageCraft screen.

The left display is where all of the JTAG ICE programming and debugging took place. The STK500 development board has an on-board ISP programming header to allow the socketed AVR to easily be programmed using AVRStudio. The JTAG ICE is a good AVR programmer as well. I’ve included a 10-pin ISP header on the AVR Internet device. This will allow me (and you) to program the ATmega16 in socket using any device that supports AVR ISP, like the Kanda dongle.

I found myself going from datasheet to user’s guide to application notes often during the development process. I was pleased to discover the Info feature of AVRStudio 4. With this feature, I could simply point at an AVR subsystem in the Workspace window and get a short description of what the subsystem was made of and how it worked. Also, being able to see the bit structure for a register or I/O location helped keep the manuals closed. Photo 4 is a doublewide shot of the result of executing a write to the USCRB USART register, while Photo 5 is a panorama of the various windows available to you during code development.