Pin output conflict using "Arduino as ISP" [SOLVED]

Using Arduino Microcontrollers
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Hi all,

I have just learned a bit on the ISP way of programming an ATMega328P with the Arduino ISP (IDE version 1.8.5), and managed to burn a bootloader to it and also upload a sketch this way. However, there are two things that I cannot find any answers for.

  • A factory fresh empty chip needs to have the fuses set, which happens when I burn the bootloader. Then when I upload a sketch (via ISP), the bootloader is gone - but will the fuses stay ?
  • Suppose I have a 328P with a pre-loaded sketch that use pins 11 (MOSI) & 13 (SCK) as high outputs, is there a safe way to connect it to a master "arduino as isp" (in order to re-program it) ? Or would I have to change the sketch output pins first via ftdi/ch340 ?

Any advice appreciated.

2

bb328:
will the fuses stay ?

Yes.

3

Thank you pert !

4

The ISP programmer first asserts reset, which puts all pins into high impedance (input) mode, so there is no issue with the sketch. Most ISP programmers also have resistors in series with all the data lines so there would be no risk even if reset wasn't properly connected.

5

Ok, I can relax then. Thank you @DrAzzy for your detailed answer !

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