Bootloading ATMEGA328-PU not working

Other Hardware 3rd Party Boards
1

A few days ago I got a ATmega 328 MCU (Not p-pu) online that have a built-in optiboot for uno 16mhz. But I need it to run 3.3v so I tried rewriting it's bootloader but it failed. It says

avrdude: Yikes! Invalid device signature.
Double check connections and try again, or use -F to override
this check.

I tried changing the signature of the avrdude.conf (both of them) but it still gives me the same error.... Is there any way to make it work so I can rewrite a bootloader (8Mhz built-in crystal)?

I'm using Arduino Uno as ISP

2

Since the m328 has been setup to use external 16MHz crystal, you need to set it up with one before you can re-program it to use the internal 8MHz clock.

Or another option is if you use an ArduinoISP version that can generate an external clock signal on a digital pin to connect to the XTAL1 pin on the m328. Check this page, Gammon Forum : Electronics : Microprocessors : Atmega bootloader programmer, see the bottom of the page about Alternate clock source.

3

From the page you gave me, it says the pin generate 8Mhz clock signal, which is not enough. But it gave me an idea. I tried putting a jumper from the arduino's XTAL1 pin to the XTAL1 pin on the MCU that is being programmed and the Blink sketch inside is working. I then try bootloading it and it works...... So thank you for your suggestion that gave me an idea.....

4

Yes, that would work too. But for ISP programming the 8MHz external would have still worked, since it is the same fuse settings as the 16MHz external.