Electronic – Read a common digital output from multiple digital inputs

bufferingconditioninginputoutput

I'd like to read a single digital output with two separate systems, each of which has a digital input. Both systems have a common ground.

In principle, since the digital output is low-impedance and since digital inputs are high-impedance, can I just tie these two inputs together at the same output without any contention or crosstalk, or must I add in some form of signal conditioning? Does this concept scale? Can I wire N digital inputs together to read a single digital output?

If not, what kind of buffering should I try to implement?

My use-case for this scenario is to wire a quadrature encoder output to both an off-the shelf PID controller and a separate system for logging ticks.

Cheers–and thanks for the..eh input.

Best Answer

Yes, in principle you can. In digital circuits, people tend to call this 'fan-out' - single output to multiple parallel inputs.

If general, when you're trying to work out how big 'N' can be, you need to consider both the static case - how much will the DC load of all the inputs drag down/up the output - and the dynamic case - how fast can the output driver charge/discharge the parallel capacitance of all the inputs. In fast CMOS systems, the latter tends to be the main concern.

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