If I want to program a new AT90USB1286 series chip via the standard 6 pin ISP header, do I need any additional components wired up at all? I'm wondering specifically about the need for a quartz crystal and associated capacitors.

The background is that I have a couple of chips that I believe may be faulty and/or counterfeit (the latter because the Atmel markings on these chips sourced from China are exceptionally faint compared to others I've bought in the UK). I want to be able to talk to the chips with the absolute bare minimum of other circuitry involved in case it's something else at fault.

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    \$\begingroup\$ I believe there are docs on programming these devices. There are also reference designs, as well. Have you attempted to find and read through either, yet? It is usually the first thing many of the rest of us do when faced with this question. \$\endgroup\$
    – jonk
    Commented Nov 1, 2018 at 12:13
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    \$\begingroup\$ I won't argue. That gets into a question about what is and is not the function of this site and above my pay grade. I'm just not motivated to go read through documentation without already seeing enough of the easier digging already performed. In fact, I hadn't seen any effort in evidence until you just responded. And it still isn't enough to get my interest to go dig more for you. That's only me, though. Everyone else has their own perspective. \$\endgroup\$
    – jonk
    Commented Nov 1, 2018 at 12:24
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    \$\begingroup\$ @Colin it's perfectly reasonable to want to be able to program or test a chip without it being fully integrated into its intended circuit. \$\endgroup\$
    – Alnitak
    Commented Nov 1, 2018 at 12:28
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    \$\begingroup\$ @Colin The question is about programming and the necessary components to do so. Not the necessary components to have a useful circuit. Nearly everything you connect wont effect programming, but the question asks about those few components that might. \$\endgroup\$
    – Matt
    Commented Nov 1, 2018 at 12:29
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    \$\begingroup\$ Some minimum number of components could make operation more stable during programming: Pullup resistor to VCC on the Reset line. 0.1uF cap on each Vcc pin. All Vcc pins connected to Vcc. All Gnd pins connected to Gnd. \$\endgroup\$
    – CrossRoads
    Commented Nov 1, 2018 at 13:10

1 Answer 1


For best results a 0.1uF capacitor on each Vcc line to the closest GND pin. This includes AVcc. A 10k ohm pullup on the reset line. The programming lines of course.

About the clock, the datasheet says the following.

The device is shipped with Low Power Crystal Oscillator (8.0MHz-max) enabled and with the fuse CKDIV8 programmed, resulting in 1.0MHz system clock (with a 8MHz crystal). The default fuse configuration is CKSEL = "1110", SUT = "01", CKDIV8 = "0". This default setting ensures that all users can make their desired clock source setting using any available programming interface.

This implies that a crystal/caps do need to be connected to a virgin chip to talk to it.

  • \$\begingroup\$ do you read "8.0MHz-max" as meaning "8MHz maximum" or "8MHz up to the maximum rating of the IC" ? \$\endgroup\$
    – Alnitak
    Commented Nov 2, 2018 at 12:42
  • \$\begingroup\$ @Alnitak These setting are for 8-16MHz, with a Ceramic resonator, slowly rising power. CKSEL3..1 are 111. CKSEL0 is 0. SUT is 01. \$\endgroup\$
    – vini_i
    Commented Nov 2, 2018 at 15:41

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