I have a newbie-question.

I have a design for a circuit, but before I design and order PCB and assemble it I'd like to double-check whether or not some assumptions are correct.

The circuit uses 3 signals to control some ICs; since most of them are to receive the same signal I simply wired those signals from the source to all ICs that need it. In this case the same 3-pin control signals are given to 8 ICs. Can this cause problems? Simply distributing the signal like that? If so, does it scale for more than this small example? If not, what would be the best way to distribute such a control signal among ICs?

Another question I have is that ICs designed to be bidirectional, can they be used in both directions on a circuit, if switched between these directions, in a live circuit, or should such ICs stay in one direction once in a circuit? Example; read in the values of a mux and then write to the same mux/demux.

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    \$\begingroup\$ Hello and welcome to the Electronics Stack Exchange. If you need help on a specific circuit, be sure to post also its schematics: it is difficult to understand how things are working in a complex circuit basing only on some words of description. \$\endgroup\$ – Daniele Tampieri Jun 28 '18 at 7:38
  • \$\begingroup\$ Thanks! The question is applicable for any circuit using control signals. The question pertains to noise, interference or dissipation of such a signal, if used for multiple ICs, rather than one. \$\endgroup\$ – Casper B. Hansen Jun 28 '18 at 9:14

What you call "reuse" of signals is usually called fanout. Fanout refers to the number of circuit inputs that can be connected together and driven by a single circuit output. The maximum number of inputs that can be driven by a given output depends on many factors, including

  • current provided by output vs. current required by inputs

  • capacitance of inputs vs. required rise and fall times

  • length of signal lines vs. acceptable noise level

If necessary, buffers can be added to drive higher numbers of inputs.

Bidirectional signal lines are often switched in direction. The data lines in a USB cable are bidirectional, for example. The usual requirement is to design the entire circuit so that only one device is driving a particular signal line at any given instant in time.

  • \$\begingroup\$ Thank you! That was right on point, and well explained! Clears everything up quite nicely! :) \$\endgroup\$ – Casper B. Hansen Jun 28 '18 at 11:51

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