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When Reverse Engineering of PCBs Becomes Reverse Analysis

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zeeglen
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Re: Programmable Logic?
zeeglen   6/9/2014 11:21:57 AM
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@ antedeluvian Do you ever have a call to reverse engineer programmed logic

Only once, an FPGA was being discontinued but the supplier had a new replacement version in the same package, and also the tools to convert the old programming to the new device.  It did not work, and because our employer had purchased the product line from an earlier defunct company we did not have any of the original design files.

My colleague knew how to convert the program files to a readable schematic (he was the digital half of our team), and i noted that the converted schematic had eliminated buffers in several circuits - the conversion tool thought we did not need multiple buffers in series.  I took one look at the original schematic and realized the multiple buffers were being used as delay elements in ring oscillators; obviously when the conversion tool removed all that 'useless' delay the oscillators stopped working.

An over-ride to the default extraneous buffer removal option of the conversion tool solved the problem.  I wrote about this in more detail in a Scope Junction blog, but...

antedeluvian
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Programmable Logic?
antedeluvian   6/9/2014 9:36:40 AM
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Glen

I have done a little reverse engineering, and I must say I admire your systematic approach and obvious patience.

Do you ever have a call to reverse engineer programmed logic like PLDs and/or micros. If so how do you go about reversing that? I once had to reverse engineer an 8048 based paging system in order to add a few functions. It was pretty difficult even with an emulator, trying to find the hooks to add the additional code. These modifications happened quite often and finally the customer came up with the source code. That made my life much easier.

_hm
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Re: Ah, yes, Daisy Systems!
_hm   6/7/2014 6:32:49 PM
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@Glen: We have done many reverse engineering for US DoD. There are some vendors, very good at it and helps us time to time.

Yes, they are demanding and painful. But US DoD pays good money.

zeeglen
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Re: Ah, yes, Daisy Systems!
zeeglen   6/4/2014 8:52:50 PM
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Glen, I take it you don't often (ever?) have the PCB layout file to work with?

Right, PCB layout files are available only to those who first created or subsequently purchased them.  The rest of us have to deduce inner layer and other hidden connections with continuity testing.


jimfordbroadcom
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Ah, yes, Daisy Systems!
jimfordbroadcom   6/4/2014 5:50:48 PM
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Which merged with Cadnetix to become Dazix - now there's a winner of a name for you - not!  Max was there way back when.

Glen, I take it you don't often (ever?) have the PCB layout file to work with?  If you did, you might have a reason to generate a netlist.  Checking the schematic-generated netlist versus the layout-generated netlist would be one more layer of idiot-proofing.  I do as much idiot-proofing as is practical because I'm usually the idiot!

I'm reminded of a Dilbert cartoon in which Dogbert tells a caller to his tech support center, "Yes, our software is idiot-proof.  The fact that you bought it is proof you're an idiot!"

Max The Magnificent
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Way back when...
Max The Magnificent   6/4/2014 4:19:28 PM
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@Glen: Remember "way back when" having to visually scour a paper plot for an elusive resistor?

I do! I do!

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