Dual TinyX313 / TinyX5 programmer board wierd!

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Hi all,


I was building a little board with a 20 pin ZIF socket on it and intended it to be able to program either ATTinyX313 or ATTinyX5, connected to a (genuine) Atmel AVRISP MKII programmer.

My problem is (don't laugh) it works! (and it shouldn't).

AFTER I tested it and found that it worked, I then looked over my circuit diagram and what I did on the board.  I made an error (the board did not match the circuit diagram) but it works anyway and I can't for the life of me figure out WHY!

Please take a look at the attached sketch.

When an X5 chip is in the socket, it has no ground, but it programs!

When an X313 chip is in the socket, it has no crystal (the fuses are set for EXTERNAL crystal), but it programs!


(click thumb for full size)

JPEG image


The crystal, BTW, is a 10.000 MHz, VCC is 5.0V and pin 10 in red is the X313 ground (not all pins shown for clarity).

I'd appreciate it greatly if someone could tell me why this thing works!



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Last Edited: Sat. Mar 16, 2019 - 05:04 AM
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the fuses are set for EXTERNAL crystal



Can you actually read the chip signature, and then read the Fuses?


The Tiny2313 and 4313 both power up as factory new set to the internal RC Osc, with the Div by 8 enabled, for a 1MHz clock.


If the Fuses were actually set for an External Xtal, and one was not provided, I would not expect the chip to function at all.


That doesn't, however, apply to all of the AVRs.

The Xmegas, for example, always power up on the internal RC Osc, and one then sets the desired clock in software.


Regarding running without a Ground.

One would have to see a full schematic of what you have hooked up to provide mu info.

Likely, however, one of the signal pins is providing a "parasitic" ground path.

(That's not a good way to run the chip)