While programming an ATMEGA328PB via ISP, I wanted to set the efuse to 0xF5. By accident, I didn't write the efuse but the lfuse instead.
Since then, I cannot communicate with the chip via ISP anymore.
I am not entirely sure which mode the IC is in right now. Pg. 47 of the manual suggests to me that it is in Low Frequency Crystal Oscillator Mode.
I did desolder the 3-pin 16MHz resonator that was used previously and connected my function generator set to 32.768Hz in squarewave mode with 5Vpp and 2.5V offset to the XTAL1 pin. (XTAL2 is floating now that I've desoldered the resonator).
I've also connected the generators gnd to my pcbs gnd.
Then I've tried to connect to the chip with avrdude set to 500Hz Baudrate. (
Unfortunately, avrdude still cannot connect to the chip over ISP.
I've also tried the same procedure with 16MHz squarewave in case the IC is in Ext. clock mode to no avail. I've also verified with my oscilloscope that the function generators signal is indeed what it's supposed to be.
Is there anything I'm doing incorrectly here? How can I unbrick the IC?
Precaution: Using HVSP or HVPP is not an option because I lack a programmer for that.