How use reset pin of attiny45 or 85 as IO

@home I program attiny45 and 85 chips with a Nano as ISP programmer. I currently program via the arduino IDE

I now have a project which needs alls 6 IO pins. This means that I really want to use the reset pin as a digital input.

I am 100% aware that I won't be able to reprogram the attiny without a high voltage programmer after the deed is done.

Provided that it is possible. What must I type in de arduino IDE so I can use:

digitalRead( 5 ) ; // this should be the reset pin

attiny pinout

Kind regards,


You need to write 0 to RSTDISBL fuse with the ICSP.

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Other option which is maybe easier is to read the reset pin as an analog input and just make sure that the voltage remains above 2.2v
There are other ways still to 'create' more IO pins depending on your application.

Program will be real simple. I have to make 5 or 6 PCBs. I can test the program in advance with a larger arduino, so I really don't need to reprogram the attiny once I programmed it. But thanks for the tip.


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