== The Main Difference Differences Between Analog and Digital Circuit Simulations ==
Analog devices and circuits operate in a continuous domain, where node voltages and branch currents can take arbitrary (positive or negative) values. These quantities can be varied continuously as a function of time. In contrast, digital devices and circuits operate in a discrete domain, where the device pins and circuit nodes have a binary state of either HIGH (1) or LOW (0) at any given instant of time.
A digital circuit simulation is an event-driven, time-domain simulation. You can define an arbitrary time step for your live [[Digital Simulation|digital simulation]] and increment the simulation time discretely, one step at a time, and manually change the state of the input(s) at each time step. It is recommended to use a time step of 20ns, which is typical for many commercially available digital devices. Or you can initiate a digital source and define a preset binary data sequence as your input, and then run a transient analysis of your digital circuit over the duration of your data sequence.
The binary states of 1 and 0 indeed represent high and low voltages (typically 3V/5V and 0V) , respectively, at the pins of a digital device. When the input pin of a digital device changes its state, for example, from low to high, the deviceâs output pin does not change its state instantaneously. It takes a finite amount of time for the device to react to the state change. This is called the propagation delay. Digital devices may have different propagation delays for change of state from low to high (TPLH) or change of state from high to low (TPHL). As you connect and cascade many digital devices, these propagation delays add up and amount to a sizable delay time. In high-speed digital circuits, where state changes may occur very fast, the accumulated propagation delays may create serious operational problems.
==Wire and Pin Values (Level & Strength)==