# ATTINY85 variants

I am using an Arduino as ISP to program Attiny chips at 8Mhz (internal). I am using the Arduino IDE as I find this easier. Some of the chips I was programming however appeared to be working at 1Mhz instead of 8Mhz. After pulling my hair out for 30 minutes thinking it was random, I realised that they have different numbers on them (Both Attiny85-20PU) but one had 1512 (works properly) and one has 1822 (does not work properly). They are both from ATMEL.

What is this number, and also how can I get around this?

• Only if the boards.txt for it has the fuses specified properly and you choose to burn the "bootloader" (which is actually just a blank or blink sketch). – Ignacio Vazquez-Abrams Sep 20 '16 at 12:10