Constructing and simulating a digital circuit in logic-sim

Components and Signals
- Definitions:
- Schematically:

Named and unnamed Signals

Important note:

Every signal used in the circuit simulation must be defined !!!
Every signal has a unique identifier

Named and unnamed signals:
Example: how an unnamed signal is displayed:
Example: how an named signal (called MyOutput) is displayed:

Defining signals

Defining signals:

Signal signalName; // Defines an unnamed signal Signal signalName( 1, "DisplayName" ); // Define one named signal ("DisplayName")
Sig( signalName, 1 ); // Shorthand for: Signal signalName(1, "signalName")

Examples:

Signal a; // Unnamed Signal a(1, "MySignal"); // The signal is identified as "a" and // displayed with the name "MySignal" Sig(a, 1); // The signal is identified as "a" and // displayed with the name "a"

Important note on Signals

Important Note:

A Signal typed variable is always an array variable in logic-sim
Furthermore:
That's why the signal out is displayed as out[0] in the circuit simulation:

Defining a serie (array) of signals

Fact:

Defining multiple signals:

Signal signalName[N]; // Unnamed Sig( signalName, N ); // Named (shorthand)
Defines the signals: signalName[0], signalName[1], ..., signalName[N-1]

Examples:

Signal x[4]; // Defines: x[0], x[1], x[2], x[3] Sig( x, 4 ); // Defines: x[0], x[1], x[2], x[3]

Using an array of signals

Ways to use an array of signals

Each individual signal in an array of signals is identified by an index.

Example:

Signal x[4]; Individual signals: x[0] x[1] x[2] x[3]
Sig( x, 4 ); Individual signals: x[0] x[1] x[2] x[3]

An individual signal is used just like any ordinary signal

Example:

Signal x[4]; Signal out1, out2; And("aa", (x[0],x[1]), out1); And("aa", (x[2],x[3]), out2);

You can pass an entire array as parameter to a (C) function (component)

Example:

Signal x[4]; Signal out; And("aa", x, out1); // Same as: And("aa", (x[3],x[2],x[1],x[0]), out);

Components
- You can use 2 types of components in your digital simulation:
- Some common built-in components:

Defining components

Syntax to define a componet:

ComponentName ( Coord, Input-Signal(s), Output-Signal(s), other-params ) ;

Note:

The coord is the coordinate on a grid
The input-signal(s) and output-signal(s) are Signal typed variables that must have been defined before they can be used !!!

Example:

Sig(sw0,1); Sig(sw1,1); Sig(out,1); Switch ( "aa", sw0, 'a', Zero ); // Location = "aa", name = sw0, key = 'a' Switch ( "ca", sw1, 'b', One ); // Initial value: Zero or One And ( "bb", (sw0,sw1), out ); // And: inputs = (sw0,sw1), output = out Probe ( "bc", out ); // Probe out

Placement of the various components:

Connecting components

Fact:

The output of a component is connected to the input of another component

Connecting the output of a Component1 to the input of another Component2:

Sig(signalX,1); Component1( coord1, ..., signalX ); // SignalX is the output signal of Component1 Component2( coord2, signalX, ... ); // SignalX is the input signal of Component2

Example:

Signal sw0, sw1, out; Switch ( "aa", sw0, 'a', Zero ); ^^ Output signal of a switch Switch ( "ca", sw1, 'b', One ); ^^ Output signal of a switch And ( "bb", (sw0,sw1), out ); ^^^^^^^ Input signals of the And gate Probe ( "bc", out );

Resulting connection made by the red signals:

Common error in connecting components: connection outputs of different components together

Warning:
When are outputs of different components connected together:
Example:

Example Program: (Demo above code)

Prog file: click here

How to run the program:

Right click on link and save in a scratch directory
To compile: cs355sim andx
To run: ./simex

Error message:

The program will compile

When the circuit simulation is run, you need see this error message:

Error (outputConectivityError): Signal[4] name = UnNamed[0] const plus source or two sources, cmp = 3 name = Or at bc There are 1 outputConnectivityErrors--Unable to Continue.

Displaying the internal display labels of the connections/signals

Fact:
Example: run the circuit simulation in the previous example
Press the function key F5 and you will see the following:

Note:

Yo do not want to display the signal labels because you will use many signals in your projects
I tell you this because it will give you some idea on how the circuit simulation works....

Grouping signals

Grouping (existing) signals

After defining the signals:

Sig(a, 10); // Signals: a[0], a[1], ........., a[9] Sig(b, 5); // Signals: b[0], b[1], ..., b[4]

you can group some of the signals together:

( signal1, signal2, ..., signalN ) = a group of signals A group of signal "counts" as ONE single signal !!

This is just like Java:

{ Statement1; Statement2; // "Counts" as ONE single statement !!! ... StatementN; }

Example:

The And-gate has the following syntax:

And( Coord, InputSignal, OutputSignal );

The InputSignal consists of only one signal !!!

To use an input of two signals to the And-gate, we group the input signals as follows:

Example Program: (Demo above code)
- Prog file: click here
How to run the program:

Signal notation

Fact:

Often, a group of signals is composed of signals from different sources
When we compose a group of signals, we often use a sub-range of signals from different sources

Recall:

Sig( a, 10 ); // Define a range of signals: a[0] ... b[9] Sig( b, 5 ); // Define signals: b[0] .. b[4]

We can compose a group of signals using a range notation x[i]-x[j] as follows:

(a[0]-a[3]) means: a[0], a[1], a[2], a[3] (4 signals !) (a[3]-a[0]) means: a[3], a[2], a[1], a[0] (4 signals !) (a[0],a[3]) means: a[0], a[3] (2 signals !) (a[3],a[0]) means: a[3], a[0] (2 signals !)

I will show you an example of range-notation of signals later (in the next webpage) where we discuss how to use the Multiplexor component in the logic simulator