JTAG Wiggler Clone
FEBRUARY 15TH, 2007 UPDATE: There was a mistake to this schematic that a kind fellow named “Per” noticed, and was corrected on February 15th, 2007. If you used the schematic after that date, you’re good to go. If used this schematic before that date and the wiggler didn’t work, this is probably why 
Per has brought to my attention that the JTAG Wiggler schematic on the “JTAG Wigger Clone” page has an error. I jumbled up the P4/P3 connections on the parallel port when I was adapting the schematic in EAGLE (the schematic is based on this one http://jtag-arm9.sourceforge.net/circuit.txt). I have fixed this error in the JTAG Wiggler schematic image, and I also posted the corrected EAGLE schematic file. Thanks to Per for bringing up the error. Sorry for any trouble this might have caused.
JTAG, is an interface (and standard) developed to easily debug embedded systems. However, you need to have a JTAG emulator to connect to this interface, and commercially they are pretty pricey.
One emulator, called the Wiggler by Macraigor, has a very simple design, and uses the parallel port. People have cloned the design of this Wiggler and posted schematics online (there are many out there). In addition, Macgraigor has free software called OCDRemote to operate these Wigglers. At one point, Macgraigor modified their Wiggler hardware by adding a connection on the parallel port between pins 8 and 15, and updated the software to check for this. Eventually, this was also discovered, and now cloned Wigglers are built with this loopback connection in place so OCDRemote can be used with it.
Other software exists to talk to the Wiggler as well, though. One of the most popular comes from a project called jtag-tools by openwince. Jtag-tools runs on both Windows (compiled with cygwin) and Linux. The project page is available here: http://openwince.sourceforge.net/jtag/
Like I mentioned, there are many Wiggler clone schematics out there. Here is a popular one I have copied into Eagle (so I can later make a board if I want):
You can download the CadSoft EAGLE schematic file here: JTAG Wiggler Schematic
Recently I built this Wiggler on a perf board. Here is a picture of it:
It works
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