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Juicebox hacking (of course)
What am I doing wrong

New MessageJuicebox hacking (of course) (modified 0 times) Wizard
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I can't seem to get a connection between my computer and juicebox through jtag. jtag fails to detect it, and after messing with things I probably shouldn't have, eventually my juicebox went into some sort of reset loop. Flashing at a rate of half a second, you know? Even after unplugging from my computer. Shutting it down and removing the batteries for about a minute or so put it back to normal.

I'm pretty sure I wired things up correctly with the cheaptag found at http://warmcat.com/milksop/cheaptag.html following instructions from http://www.elinux.org/wiki/JuiceBoxJTAG EXCEPT I soldered to the opposite side of the board, because it was easier. I successfully tested connectivity, so I know that the back pads connect to the dots on the front.

I eventually managed to compile jtag in cygwin, and get it to access the parallel port directly. I forget exactly how I did that, it being a couple months ago, before this board went down.

Anywho, in a classic "my car is acting funny and I don't know why" problem, my juicebox is acting funny and I don't know why.
Can anyone suggest some ways I can test the connectivity here? Maybe run a high on one of the lines? Manually tap out a couple bytes in some archane morse code?
My cable is 45 cm, but the suggested length is max 30 cm. Should that really make such a difference? Cutting it down is a less desirable solution, but reasonable if it'll help.

Thanks.

07-18-2006 16:40:49

New MessageRE:Juicebox hacking (of course) (modified 0 times) jbfan
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The cable you are using is directly connecting the JTAG signals to the PC parallel port. The parallel port a 5 volt device while the processor on the JB is a 3.3V device. This is probably your problem.

What is needed is a buffer between the 5V outputs and the 3.3V inputs.

A "Wiggler" clone will do what you need;
http://jtager.sourceforge.net/doc/circuit.txt
I would suggest using a 74LVT244 (5V tolerant inputs) in place of the AC244 in the schematic.
The circuit uses a somewhat specialized device (DTC114) but I have found that just about any NPN switching transistor will work.

Hope this helps.

-J

07-18-2006 17:41:43

New MessageRE:Juicebox hacking (of course) (modified 0 times) prpplague
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i've updated the wiki pages with some notes reminding people that the juicebox jtag is 3.3v only!
07-19-2006 07:02:42

New MessageRE:Juicebox hacking (of course) (modified 0 times) Wizard
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Curses. I could have sworn I saw a success story using the cheaptag. Oh well, I'll give the wiggler a try, if I ever get around to it.
Thanks a lot, guys.
07-19-2006 15:55:00

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