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I would like to connect several microcontrollers as shown in the circuit diagram below. The software makes sure that the PA1 pin always has the low or floating state. It's a kind of open drain control. However, the ATtiny1616 still has a small voltage, up to 0.3×VDD, in its low state. This voltage is slightly different at each pin due to temperature differences and tolerances. This could lead to high currents if more than one pin switches to low. Would the circuit still work? If so, why isn't the small voltage difference from pin to pin a problem?

schematic

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  • \$\begingroup\$ You should be OK. That is most likely a programmable pin, and 0.3 * Vdd is the guaranteed maximum voltage for a logic 0 when the pin is used as an input. If there is an output spec, it would indicate the maximum voltage for a logic 0 with a specified current. This would indicate how effective it is at pulling low, not that it will put out a voltage (assuming it was programmed as an open drain). \$\endgroup\$ – Mattman944 Apr 22 at 13:08
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You have basically configured an I2C bus of sorts with each device on the bus pulling the line low as required. I wouldn't be too concerned about current moving between multiple low pins as it will likely be in the order of milli to micro volts but if you are concerned you can always add series resistors on each PA1 pin before connecting to the output bus line.

If the output is just for detection by a separate high impedance input device then you can even raise the 10K pullup value to save on power draw.

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  • \$\begingroup\$ Depending on application, it's not advisable to go beyond 10k for EMC reasons. Particularly not with AVR having a bad reputation when it comes to EMI susceptibility. \$\endgroup\$ – Lundin Apr 24 at 11:54
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Often forgotten, but there will be no issues in this case at start-up with connecting ports together.

After Reset, all standard function device I/O pads are connected to the port with outputs tri-stated and input buffers enabled, even if there is no clock running.

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