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I flashed ATtiny85 once with simple program blinking for 1 second. F_CPU = 32768. I set low fuse byte to 0xe6 with avrdude. According to datasheet 6 = 0b0110 CKSEL is intended for low frequency quartz oscillator. In my case it is 32khz. Capacitors have 5ns. LED blinks with expected period, but both programmers usbasp and avrispmkii cannot see the chip anymore. I tried to turn on JP3 on usbasp and was playing with avrdude -B option trying various values from 2 to 1500. Outcome is the same - avrdude prints 0xc9. Meanwhile same model chip is flashable with 10mhz quartz by both programmers (low fuse = 0xef).

I saw somewhere similar post and recommendation was to keep RESET pin low. I didn't get how this would help and what actually I should do. I was connecting RESET with GND.

I have lots of 32khz quartz. I tried to connect several of them in parallel in hope to double frequency ;) and didn't notice anything. The chip doesn't start with 10mhz quartz.

Is it possible to make adapter for external clock to fool an AVR chip and simulate quartz generator at higher frequency, but compatible with CKSEL 0b0110?

I am not sure about SUT fuses too. There are several options available. Maybe problem is caused by them?

I think I chose correct option (avrdude lfuse gets = 0xef):

0b10 32K (32768) CK 64 ms Stable frequency at start-up
Daniil Iaitskov
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  • Did you use the debugger at all? The ATtiny85 supports debug-wire and SPI programming. If you switch to the debugger then the part won't program until its switched back to SPI mode. This can be done with a menu in Atmel Studio. – user4574 Jan 07 '21 at 18:42
  • Did you change the hfuse? If so, you have likely "bricked" the part unless you have a HV programmer available or something that supports debugWire like Atmel-ICE. – jwh20 Jan 07 '21 at 19:09
  • I didn't touch hfuse at all where debug bit is. – Daniil Iaitskov Jan 08 '21 at 08:27
  • Please post your avrdude output with -v option turned on. Does it sets SCK frequency correctly by -B switch? You can – NStorm Jan 12 '21 at 18:06

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