<b>Setting the Input</b>
The simplest input device for digital circuits is the "Digital Input" with the keyboard shortcut N. For the basic input port, click on the up and down arrows with the selection arrow to toggle its value between 0 and 1. Or double click on the input port to open the device's property dialog and set or change the input's value. [[RF.Spice A/D]] offers a number of other input devices for [[Digital Simulation|digital simulation]]. With the "Toggle Switch", click on the switch to change its value. The button changes with each click of the mouse. The "DIP8 Switch" has eight output pins, each of which are controlled by a separate switch. Clicking on the switches will toggle their output values. With the hexadecimal "Keypad", click on one of the 16 buttons to select a value from 0, 1, ..., 9, A, B, ..., F. A "Digital Source" allows you to define a sequence of binary values as a function of time (or time step index).
[[File:B2TUT4 1.png|thumb|400px| A simple digital circuit with three digital inputs and one digital output.]]
The simplest output device for digital circuits is the "Digital Output" with the keyboard shortcut O. A digital probe device does the same function. All input and output port logic levels are shown in the input and output ports in hexadecimal notation. For single wire probes, the probe values 1 and 0 mean logical High and logical Low. The value ? means indeterminate, i.e. the program cannot determine the signal value. A strength of S is a strong signal, strength R is for resistive strength, Z for High Impedance, and ? for unknown strength.
If "Circuit [[Animation]]" is activated for [[Digital Simulation|digital simulation]], you will see the logical state of all wire during a simulation as text. If "Circuit [[Animation]]" is turned off, you can view the logic level and strength of any wire in the schematic window by using the "Probe Tool". You can access this tool either from the [[Schematic toolbar|Schematic Toolbar]] or from Edit Menu or simply using the keyboard shortcut Ctrl+Alt+P. In the "Probe Mode", place the tip of the logic probe on any wire and depress the left mouse button to see its logic level and strength. If the logic probe is probing a digital bus, then the value of the bus is the hexadecimal value calculated by making bit 0 of the bus the least significant bit.
For output devices, the device name and decimal or hexadecimal format can be edited. Choose "Assert High" or "Assert Low" to determine the polarity setting of the device.
[[File:b2MAN_Fig38.png|thumb|300px| Simulation Time Options Dialog.]]
<b>Running a Live Interactive [[Digital Simulation]]</b>
Set up the input values and set the time step you desire from the Simulation Time Options dialog. To open this dialog, click the Step Interval Settings [[File:b2Interval_Tool.png]] button on the [[Main toolbar|Main Toolbar]], or select the Time Options item of the Simulate Menu, or use the keyboard shortcut Ctrl+I. A typical time step for digital circuit simulations is 20ns. Click the Step [[File:b2Step_Tool.png]] button to start the simulation. The simulation time is incremented by one time step. The current time is displayed in the simulation toolbar next to the control buttons. You can view the logical state of the wires and device pint either using the logic Probe Tool or by Circuit [[Animation]]. The values of input and output devices are displayed, too. You can change the values of input devices in real time. Click the Step [[File:b2Step_Tool.png]] button once again to increment the time by another time step. The Walk button starts the simulation but increases the simulation time by the walk factor, which can be set in the Simulation > Time Options menu. Click the Strop/Reset [[File:b2Stop_Tool.png]] button to reset the time to t = 0.
With [[RF.Spice A/D]] you can also view live digital timing diagrams during a live [[Digital Simulation|digital simulation]]. Click on the "Show/Hide Live Digital Timing Diagram" [[File:b2Timing_Tool.png]] button in the [[Schematic toolbar|Schematic Toolbar]]. Initially nothing happens. A soon as the [[Digital Simulation|digital simulation]] starts, a graph window opens up at the bottom of the screen that shows live timing diagrams for all the input and output devices. As you continue to step the time, these graphs expand. Similar to other graphs, the digital timing diagrams have their own settings dialogs in the Toolbox. Note that the timing diagrams are updated only when a change occurs in your circuit.
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