How do they make Verilog code for unknown ICs?

Swift Griggs swiftgriggs at
Mon Jun 20 15:47:47 CDT 2016

On Mon, 20 Jun 2016, Ian Finder wrote:
> Some PALs, PLAs, and GALs will yield the fuse map if you try and read them
> with a programmer. This makes your job really easy. Take the fuse map and
> compare to the original data sheet. Cool beans.

That sounds like magic. I'm reading about what "fuse map" is, now. That's 
a new term for me. 

> Some have the security bits set- in this case you would use a home-made 
> test setup to stimulate enough test conditions to build a truth table 
> that would allow you to infer the underlying logic.

Hmm, so there is something akin to "copy protection" even at the chip 
level. Ugh. I'm not surprised.
> If the part is registered, then things get tricker. For that, I might 
> take substantial in-system dumps with a logic analyzer (My favorite 
> beginner LA is the Agilent 16700, which comes with DOOM preinstalled, so 
> you know it's good stuff)

Oh, cool. I was just browsing for one a few days ago. I was looking at the 
ones from Saleae and Tektronix. I'll have to check that out. If they were 
cool enough to pre-install Doom, I think we have a winner. :-)

> ROMS are easy- once you read a bit about how HDLs work, you will be able 
> to build one. Many languages offer functions to help with these (see 
> readmemh and readmemb in verilog)

I actually did burn some ROM code in college. I remember it being fairly 
easy. However, I would look like a stunned fish if someone asked me to 
reverse engineer one.

> Things get more complicated quickly- this is a deep topic and not 
> something that can be covered quickly. I suggest you start with the two 
> books I linked, and if you like them, there are a lot more around. Any 
> edition should be suitable- get or find whatever is cheapest.

Oh good lord, I'm so out of my depth already. However, it's still 
interesting and I'm still trying (I'm stubborn that way). I've got to get 
the simplest basics down before I dive in all the way with a "real" book. 
I'm going to try to stick with my digital logic self-refresh first, but 
this Verilog business is awfully cool. I will be sorely tempted to come 
back to this same point, I'm sure.

> We have not touched yet on practical things, like how to interface 
> modern 1.8v FPGA I/O lines with 5V TTL logic- that is a topic for 
> another day.

Hmm, I never even knew of that problem, but after doing a bunch of analog, 
I get the impression that would create a lot of hassles, especially if you 
were just trying to duplicate some already laid-out logic, but it was all 
at 5V... 


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