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Jtag - How Does It Work?


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#1 DJeX81

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Posted 19 March 2010 - 06:21 AM

Now that I've gone through and made my own LPT cable and soldered it all to the xbox motherboard and JTAG'd it, I'm curious now to how it all works.

I know a JTAG is for testing circuit boards and such and so I'm assuming that when one JTAG's a vulnerable xbox there using the vulnerable JTAG test port to read the nand and write to it but I'd like to know why certain spots need to be soldered on and how was it ever figured out that these spots were needed to perform this hack. I guess one could get the motherboard schematics and devise a way from that but are those available for each motherboard version?

I guess what I'm most interested in is why do you need to add theses wires (http://www.digitalre...09/12/Fdjmi.png) or (http://www.digitalre.../12/diagram.jpg). What are there purpose?

If there's a site that describes why the JTAG hack works then I'd be glad to take the link and give it a read. I'm just interested in this all and since I'm not highly educated in electronic circuitry I'd like to learn more.

Btw im not a complete noob asking for info I'll never understand. I do networking and computer repair for a living tongue.gif

Edited by DJeX81, 19 March 2010 - 06:22 AM.


#2 sdtrojans3

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Posted 19 March 2010 - 06:30 AM

i have wondered this same thing, and the only thing i can figure out is either A) the person who figured it out is someone on the inside smile.gif , cool.gif they have no life other than looking for stuff like this with endless supplies of boards, C) brilliant person. D) combination or all of the above. lol it baffles me, but i give many thanks to the people who did figure this out

#3 cRaCKwHoRe

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Posted 19 March 2010 - 11:35 AM

First of all the three JTAG wires have nothing to do with being able to read and write to the NAND. We have always been able to do that. However, with the JTAG wires in place we are able to use the SMC (through the JTAG wiring) to modify the bootup sequence to run XeLL. I'm not going to go into a long, drawn-out explanation of how it works. You can read about it here: http://free60.cvs.so...amp;view=markup.


#4 DJeX81

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Posted 19 March 2010 - 11:14 PM

QUOTE(cRaCKwHoRe @ Mar 19 2010, 11:35 AM) View Post

First of all the three JTAG wires have nothing to do with being able to read and write to the NAND. We have always been able to do that. However, with the JTAG wires in place we are able to use the SMC (through the JTAG wiring) to modify the bootup sequence to run XeLL. I'm not going to go into a long, drawn-out explanation of how it works. You can read about it here: http://free60.cvs.so...amp;view=markup.


Oh wow thanks. I'll give it a read.




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