Board repair logs indicate this part commonly failed. These chips are a bit unusual in several ways. First, they use 12 bit words. Second, code protection intentionally leaks a 4 bit xor of the 12 bit words. Therefore, even with protection enabled you can glean quite a bit about the firmware.
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Board repair logs indicate this part commonly failed. These chips are a bit unusual in several ways. First, they use 12 bit words. Second, code protection intentionally leaks a 4 bit xor of the 12 bit words. Therefore, even with protection enabled you can glean quite a bit about the firmware. We went with a UV attack, but this might also make them vulnerable to programming one nibble at a time and observing the xor difference.
Anyway, all chips are dumped as received "protected dump". All chips were still packaged when received. The first three were easy: But was received in poor condition: Pins straightened, but pin 1 still missing. So instead fitted something more flexible: and got a dump after de-protecting. We hoped that de-protecting was going to shed more light on this but did not.
Its unknown if this was accidentally erased at some point, the silicon is damaged, or what. Finally, we do not believe we accidentally programmed this. No die damage is visible. We do not yet have a theory as to what happened to this chip.
To summarize, , , and were dumped successfully. We believe was corrupted before we got it. Similarly, was received bad and its unclear if we can fix it. Enjoy this post? Please support us on Patreon or Indiegogo! Posted by.
We popped it into a reader and it spit back a scrambled protected dump, so this was plausible. After some discussion, we decided this was close enough to proceed. However, HSH has a copyright, and the sample has a copyright as well. So all evidence points that this really is a PIC16C55 despite the different masks. We secured a sample and applied a mask: Which after 15 minute or so of UV erasing had lost protection but retained the original data.
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