Basics of Digital Simulation

   1.  Digital LOG is simulating your circuit constantly, even as
       you edit.  Every wire has a "state," corresponding to the
       voltage on the wire:

            Zero        a wire connected to ground,
            One         a wire connected to Vdd,
            Weak one    a wire connected to Vdd through a pullup resistor,
            None        a wire that is floating (not connected)

   2.  You send signals into the circuit using switches, and read
       the state of the circuit using displays such as LED's.

   3.  If you ever drive a node (wire) with both One and Zero at the
       same time, the node starts flashing to indicate a "conflict."
       Since this is not an analog circuit simulator, digital LOG can
       not represent the correct value of the wire, so it flashes the
       wire and picks either One or Zero arbitrarily.

   4.  Digital LOG uses a "unit delay" simulation model.  All gates
       are considered to have the same delay, whether they are NAND
       gates or complex counters.  (The STABILIZE command may change
       this behavior for short periods of time.)

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