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I'm planning to make a small circuit with a ATtiny85V-10PU. As the pins on this chip are very limited, there are just enough for what I'm planning to do, so all pins will be used for in- or output with LEDs and stuff connected.

When including a ISP connector to this pins, my opinion is, that connected things like LEDs etc. would use the ISP data as power source and maybe the connection could not work to programm my chip (low voltage or something like this). Is there any prevention circuit I should include to be on the safe side, or am I fully wrong?

Is there any best practice, nothing circuit specific?

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    \$\begingroup\$ Have you read Atmel AVR042: AVR Hardware Design Considerations? It's going to be difficult for anyone to give you specific advice if you don't also provide specific explanations of what the "things" connected are. \$\endgroup\$ Commented Jan 21, 2013 at 17:40
  • \$\begingroup\$ Thanks for this document. Didn't know about it. To the "what things" question: I'm searching for some kind of best practice nothing circuit specific. \$\endgroup\$ Commented Jan 21, 2013 at 17:50
  • \$\begingroup\$ Well, obviously, don't have sources which can't be disabled driving pins in ways that would conflict with ISP, unless you do so through large enough series resistors that the ISP/ATtiny reply can over-ride them. Probably if your ATtiny can drive the loads, there exists an ISP implementation which could as well (after all, you can make an ISP with a similar chip, and the added load of the target chip isn't much). \$\endgroup\$ Commented Jan 21, 2013 at 17:54
  • \$\begingroup\$ New link for AVR042. \$\endgroup\$ Commented Apr 1, 2016 at 23:27

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There are no general best practices. For each pin, consider what will happen if it is forced high or low by the programmer. Will it break anything in your circuit? How much current will the programmer have to source or sink to get the voltage to be at ground or Vcc? Will this exceed the specifications of your programmer?

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Get a through hole version of the ATTiny85, and your other components (including a programming header). Wire it up on a breadboard and verify one way or the other that it works (or not) in your context. This is called prototyping, and can be helpful in determining whether a design is viable prior to going to production.

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  • \$\begingroup\$ This was planed, but I wanted to know if there is any "best practice". For example analog to the "capacitor directly at power pins"-best practice \$\endgroup\$ Commented Jan 21, 2013 at 17:49

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