PIC18F14k22 and fuses

spilz · Joined: 30 Jan 2012 Posts: 219

Hello everyone

I’m working on the PIC18F14K22 and I’m confused about protection fuses.

What I would like :
- Writing the code only once
- disable writing a new bin
- disable reading the bin
- disable reading from outside the EEPROM
- disable fuses clearing
- keep enable reading and writing the EEPROM from the internal software

Any other protection ??

I tried to read datasheet and topics but I was very confused

Can someone help me ?

Thanks in avance

temtronic · Posted: Sat Nov 16, 2024 3:46 pm

re: Any other protection

Not really 'protection' but if you sand off the PIC's model number and date code it'll slow down someone from reading what you have.......1st they have to figure out WHAT the blob of epoxy actually is...

Have to admit I don't use 'code protection'. I remember the very early PICs ( the ones with quartz windows ) you COULD read even if protected. What looked like garbage ,once you did some 'bit manipulations', the real machine code 'magically appeared'.
I assume Microchip has added better security since then....

Ttelmah · Joined: 11 Mar 2010 Posts: 19539

You can always reprogram a flash chip.
If a chip is full erased, all the fuses go off, so it can be reprogrammed.

So your very first wish, can't be done. The only way to have a chip that
can be programmed only once, is to have a OTP chip. Current PIC's are
not OTP.
This fuses are individually protected, _except_ for a full erase. The point
is that you do this, and you start with a blank chip. No code, and no fuses.
Such a blank chip can be programmed with new code. The same applies to
your second line. WRTC enables the fuse protection.
The third, is exactly the point of the code protection. On modern chips this
is very good.
It is always possible to read the code, if you spend enough money. The old
standard get around, was to use an electron microscope on the memory.
The internal EEPROM, can be read/written by the internal software even
when protection is enabled. Would be pointless otherwise.
23.3.2 in the data sheet,

jaka · Joined: 04 May 2014 Posts: 36 Location: Finland

Ttelmah · Joined: 11 Mar 2010 Posts: 19539

Yes. These have a single word of the config memory, that needs different
commands to access, and contain a number of bits affecting various
features of the programming. I'd guess they are actually flash memory,
but without he charge pump connections for erase. So once set, except
for age degradation after perhaps 20+ years, they are OTP.
Does give effectively OTP behaviour on the flash memory.