# ATtiny13A cannot be programmed anymore with Arduino as ISP at 500 Hz

My ATtiny13A fuses are set to use the internal 128 kHz clock without clock divided by 8. I found online an ArduinoISP sketch that allows me to program it with that clock speed. But then I uploaded some code with those lines at the start of my main() to set the clock division factor to 256:

CLKPR = (1 << CLKPCE); CLKPR = (1 << CLKPS3);

So my clock should normally now runs at 500 Hz. I guess it works, but I now cannot program my ATtiny13A anymore, it gives me unexpected signature error.

I found this ArduinoISP sketch online: https://github.com/lmpipaon/ArduinoISP_slow_SCK

Seems nice but it says it does not work with the 256 prescaler, which is what I need. When I try nevertheless to use the 256 prescaler with 600 baud rate in the ArduinoISP sketch, avrdude (avrdude -b600 -cstk500v1 -P /dev/cu.wchusbserialfa130 -pattiny13 -e -U flash:w:lowVoltage.hex) still gives me unexpected signature errors.

I also tried adding -B 8000 or -B 10000 with my upload command but apart from giving me different device signatures, it does not upload my code.

• Holding the device in reset while powering it on will prevent the code from running. – Ignacio Vazquez-Abrams Aug 10 '16 at 15:01