AVR JTAG ICE - Comparisons
Why would you choose the ECROS Technology AVR ICE-Cube rather than the Atmel JTAG ICE or some other "clone" JTAG ICE? Why wouldn't you build your own JTAG ICE interface? This page presents information to help you make the best choice.
Comparison with Atmel's JTAG ICE
Comparing with other "Clone" JTAG ICEs
Building your own JTAG ICE "Clone"
Comparison with Atmel's AVR Dragon
The ECROS Technology AVR ICE-Cube is different from the Atmel JTAG ICE in the following ways:
- It costs a great deal less.
- It does not have a separate power supply and takes power from the target system (see Power Supply in Technical Details for more information).
- It works from 3 volts to 5.5 volts, but not with the very low voltage MCUs.
- It does not have level-shifters, which is, of course, OK when it is taking power from the target as logic levels will necessarily be the same.
- It is very much smaller and lighter.
- It is packaged very differently, perching on the target system connector rather than sitting on the bench in its own box.
If you are working with very low voltage MCUs or need the assurance of an Atmel-supported product, your only choice may be the Atmel JTAG ICE. Commercial users may want at least one Atmel unit but could make use of "clones" to increase the number of in-circuit debugging stations available at low cost.
Much of the information needed to build a JTAG ICE "clone" is available on the Web. Several have become available during 2004 from various sources. ECROS Technology has examined one of these and found it to be poorly designed (which precipitated the design of the ECROS Technology AVR ICE-Cube). If you are choosing a clone, below are some things you should look out for. The links take you to technical details of the ECROS Technology interface, where you can read more about these issues.
- Quality of PCB Design - Does the design of the printed circuit board follow good engineering practices? Will it have low emission of and sensitivity to EMI?
- Voltage Range - What range of target system supply voltages does the adapter support?
- Decoupling and Noise Isolation of Power Supply - Is the power supply of the adapter properly decoupled? Is there protection from noise passing between the adapter and target system?
- Flash loader - Is the adapter's flash loader fully functional? Does it activate when it is supposed to? Can you activate it manually?
- Measurement of Target Voltage - Is the target voltage reported correctly?
- Packaging - Is the adapter packaged in a way that is convenient to your work layout?
- Documentation - does the vendor tell you everything you need to know to get the most out of your JTAG ICE?
If you cannot spare a little power for the ICE adapter or don't like the packaging of the AVR ICE-Cube, you may be able to find another suitable clone. But, do investigate the quality of the design and documentation before spending your hard-earned money!
There is nothing very challenging in building a JTAG ICE clone that can be made to work in most circumstances. If this sounds like an interesting project, go for it. However, if you need the JTAG ICE interface for what it can do, as opposed to the experience of making it, consider purchasing one. If you value your time even as low as minimum wage, you will not be able to save anything by building your own. Using a well-designed commercial interface will also avoid the chicken-and-egg problem when something is not working and you're not sure whether it is the target system or the ICE interface that is at fault.
The AVR Dragon is a departure by Atmel from the solid but expensive ICE tools such as the JTAG ICE Marks I and II. It is cheap ($52.00) but rather flimsy. It would seem to be targetted at the enthusiast more than the professional user. That having been said, if you're an enthusiast you should give it serious consideration. The list of devices it supports is not extensive, but it will probably grow. The Dragon supports debug-WIRE, which means it supports on-chip debug for newer and low pin count devices such as the ATmega48/88/168 and ATtiny13, ATtiny25/45/85 and ATtiny2313, which do not have JTAG interfaces. On the other hand, it does not support on-chip debug for devices with more than 32 kbytes of Flash memory! This is probably a marketing decision by Atmel rather than a technical limitation, so this is likely to be a permanent draw-back. You will prefer the AVR ICE-Cube if you're using an ATmega64 or ATmega128 ot if you need the small footprint and built-in cables (the Dragon does not come with cables and you'll need to find a 10-way ribbon cable as well as a USB cable). To find out more about the Dragon, you will have to install AVR Studio 4.12 with service pack 3 or newer as the only available documentation appears to be in the help system. Don't be fooled by the odd claim that the Dragon has a "prototyping area". This is just somewhere you can solder a zero-insertion force socket and wire it up so that the Dragon can act as a programmer for certain DIP devices. If you want to do this, you'd better glue the Dragon down to something solid.