Simple Question Regarding Sequential Logic

Thread Starter


Joined Mar 6, 2010
Hey guys, I have this very basic problem that I can't seem to figure out. I'm taking this course where we're learning from the book "The Elements of Computing Systems", and in it they use a language called HDL in order to simulate hardware.

Anyways, I'm trying to build a 1-bit binary cell using it (this is for a lab we did last week, and I didn't know how to do this then, so I figured I'd get it clarified now), and I don't understand how you can actually code it so that the input of the multiplexor is the input, AND the output of the circuit.

Basically, what I have coded is simple too:
Rich (BB code):
CHIP Bit {

    IN  in, load; //input pins
    OUT out;    //output pin

    Mux(a=in, b=out, sel=load, out=Din);
    DFF(in=Din, out=out);    
However when I try to run that, the simulator tells me that I can't load the Mux chip using the out pin as input, since it hasn't actually "made" that yet. In a real circuit, I realize that if you're just turning this on for the first time, out would be 0 (or low), and therefore wouldn't matter, but I can't just say that while coding.

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