USB programmer 3.3V and 5V

Hi guys,
I was wondering if the new USB ISP programmer also can program with a Vcc of 3.3V as well as 5V.
Right now I have the old pololu programmer but if the new one it has this feature I can use to program also other AVR I have around in my lab.

The Pololu USB AVR Programmer can program AVRs that have a Vcc of 5 V, but will not work when programming AVRs with a Vcc of 3.3 V.

The programmer requires the AVR to generate a high signal of at least 4 V on the MISO line, and if your AVR’s Vcc is 3.3 V it will not be capable of doing that.

The programmer outputs a voltage of ~5 V on its MOSI, SCK, and RESET lines, and (depending on your model of AVR) those signals might end up powering the AVR because they are significantly higher than the Vcc of 3.3 V.



That 4V threshold David mentioned is the guaranteed high level of the microcontroller on the programmer; however, chances are that 3.3V will still get treated as a high. The outputs from the programmer (SCK, MOSI, RESET) will be at 5V, though, so you would have to put in voltage dividers to get to 3.3V signal levels or at least in-line resistors to limit current into the 3.3V device. So, if you have some target you don’t care about too much, you could try it, and while I suspect that success is likely, it’s not guaranteed.

- Jan

Hi Ben,
yes right thanks for the tips.
I will keep you posted, if I fry it I will buy another one :laughing: