Re: AVR trivia question


Ulf Samuelsson wrote:

I think that is a security thing.
If you can enable JTAG, you can read out the contents.

If I really want to protect that, I would cut the pins.

If you really want to copy the content, you would remove the chip and
go for parallel probe anyway.


The parallel programming will allow you to erase the chip, but not read it
out.

Why doesn't Atmel simply disable jtag reading, but not erasing. AVR's
jtag is unreliable, since it's subject to software and hardware
gitches. I have a prototype board that lost jtag immediately after
messing with the fuses. My customer and I are nervous that software
gitches can render the chip useless.



When you do a full chip erase you can erase the JTAG disable so you can
use:
* High Voltage Parallel programming: (That is difficult to use for
most
customers)
* ISP.

Exactly, especially when it's difficult to isolate port B and D
in-circuit.

I would suggest a simple chip erase mode (+12V to VCC and RESET) to
erase the chip and put it back into factory defaults.

High Voltage Serial programming is available on some devices.


--
Best Regards,
Ulf Samuelsson
This is intended to be my personal opinion which may,
or may not be shared by my employer Atmel Nordic AB

.

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