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I'm a total newbie fooling around with a project of mine.

I want to use an MCP23017 I2C port extender (Data sheet) for my Arduino project.

The chip has three hardware pins that must be externally biased.

I apologize if the question is silly, but, can I just connect the pins to V+ or GND, or do I need to put a resistor in series to limit the current? I looked around a bit but I wasn't able to find an answer.

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  • \$\begingroup\$ Don't forget the reset pin as well as the three address lines, looks like that should be tied high as well. \$\endgroup\$
    – PeterJ
    Commented Aug 24, 2014 at 11:40
  • \$\begingroup\$ yup, good catch :) thanks, and thanks for fixing the link, too! \$\endgroup\$
    – garph0
    Commented Aug 24, 2014 at 11:51

1 Answer 1

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Yes you can directly connect these pins to GND or V+.

The reason you did not find this explicitly stated is that it is standard that a high-impedance digital input can be connected directly to a logical 0 or 1. When a resistor was needed this would be stated explicitly.

Using a resistor instead of a hard connection might be convenient when you need to change the address on a finished PCB: you can short the pin to the opposite supply rail without damaging anything.

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  • \$\begingroup\$ "Using a resistor instead of a hard connection might be convenient..." This is often a zero-ohm link/resistor which doesn't impose significant resistance but is useful for its standard form factor. \$\endgroup\$
    – Benjamin Crawford Ctrl-Alt-Tut
    Commented May 8, 2020 at 19:58

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