How to disable serial program downloading SPI with AVRDUDE

Using Arduino Avrdude, stk500, Bootloader issues
1

Hi,

I'm using AVRDude to program an arduino Nano - using a Sparkfun AVR pocket programmer. I'm able to set fuses and lock bits, but the 'Serial program downloading (SPI) enabled; [SPIEN=0] *' bit does not take the disable setting.

I'm setting:

  • the Low fuse as: FF
  • the high fuse as: FA
  • the efuse as : FD
  • the lock bit as: C0

here's a screen shot from a fuse calculator:

image
image1511×645 40.2 KB

All of the settings 'take' except the high fuse, which comes back as "DA"

AVRDUDE will program all the other fuses but not the high fuse (AVRDUDE message says: avrdude.exe: verification error, first mismatch at byte 0x000 0xda != 0xfa) -

when reading back the fuses - it shows DA as the high fuse setting (which means that Serial program downloading (SPI) is enabled (and I can't seem to disable it).

I'm wanting to lock down the chip so a flash erase is necessary to read program/write to it

thanks in advance!

2

From the datasheet:

And to protect your code, you don't need it.

From an very old project that I did (Arduino Nano)

  1. Set lock bits to 0
  2. Not sure why I did it (too long ago) but I did set BOOTRST to 1
3

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