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DesignWorks is a logic schematic creation and simulation program by Capilano Computing. It comes with many circuit symbols and models that allow you to create logical circuits. This tutorial goes over a few hints to successful use of DesignWorks and walks through a simple example circuit.

Introduction:

DesignWorks is a logic schematic creation and simulation program. It comes with many circuit symbols and modelsthat allow you to create logical circuits. We will be using DesignWorks Professional by Capilano Computing.

For another tutorial, see the Capilano website: http://www.capilano.com/DWLiteManual/5min.html

Anatomy of a circuit (some terminology that may be useful as you read through this doc)

Circuit anatomy

This figure shows circuit terminology that will be used throughout this tutorial.

Component libraries to use:

DesignWorks comes with libraries of logic components, such as NAND gates, Multiplexors,and Adders. Because you will be using DesignWorks to understand basic logic design, you will not need to use the componentlibraries that model real components you can buy and use on a circuit board. Instead, you will be using the components in thefollowing four libraries : Pseudo Devices.clf, Simulation I0.clf, Simulation Gates.clf, Simulation Logic.clf.

Designworks do's and don'ts:

  • Do save your work often.
  • Do save intermediate results. If you have a nice working section of your circuit, save a copy so that you can get back to itin case anything goes wrong as you add elements. DW is a powerful piece of software, but does occasionally get into a wiringsnit.
  • Do not drag large sections of wired components to move them. Dragging often causes wires to reattach themselves in undesirableways to selected components or things they are dragged over. Instead what you want to move, cut from the current location, andpaste in the new location.
  • If your circuit is behaving strangely, use the ? tool to debug your circuit. Starting with the location of the strangevalue, probe connected wiring working from outputs back to inputs. Test pins and the wires that appear to be connected to them. Whentesting pins, the ? tool must be touching the very tip of the pin, otherwise you will see a Z output. If you find a loose connection,use the zap tool (see Deleting Wiring below) to delete and reattach the connection.
  • Do test wiring right after it is placed. (See Testing Wiring below.)
  • Do learn what all the simulation values mean. (See Simulation values: (0, 1, X, Z, or C) below.)
  • Do use named signals to make connections rather than long stretches of wiring. When using named signals, spaces are relevant,so be very careful that the name matches exactly.

Designworks reference notes:

  • Using Component Libraries: On the right of the DesignWorks display, you will see a parts palette. You can select libraries ofcomponents to choose from by selecting the name of the library you want to use from the library selection drop-down list. You can alsoselect “ALL LIBRARIES” to be able to choose from all loaded component libraries. You can load and unload new libraries from the“File/Libraries” menu.
  • Placing and moving components: Double-click on the component in the parts palette to the right of the screen. Your cursor willchange into an image of the part. To get out of parts placing mode, tap the space bar. You can move devices around, by clicking on themand dragging them to a new position. In order to move a switch type device, you must select it while holding down the SHIFT key, andthen move it. You can also move components by selecting them, and then using the arrow keys to move them in discrete intervals. Whenmoving groups of components, only move in discrete steps or cut and paste.
  • Orienting components: To orient components so that the output and input pins face the direction you want, use the arrow keyswhile the component is selected, and before you place it. The arrow keys will flip both the vertical and horizontal orientation of thecomponent.
  • Wiring: To create connections, position the pointer near the endpoint of a pin or wire and drag away toward the other endpoint.If you hold down the control key it will change the type of routing to route down and over, rather than over and down. Using the Altkey while drawing a wire, will create a three segment route. CTL and ALT can be used together to combine the effects.
    • Wiring by Signal Name: You can connect a named signal to a pin by selecting the Text Cursor (letter A in the toolpalette), and clicking the pencil at the end of the pin. (Clicking in the middle of the pin creates a pin number). With the end of thepin selected, place a label that matches the signal name you want to connect. Note that a physical line will not be drawn in thiscase. When using named signals, spaces in front of, within, and after the name are relevant, so be very careful that the namesmatch exactly.
    • Testing Wiring: Once the connection is made, test the connection by clicking on the signal route and noting theyellow highlighted path. The highlighted portion should extend all the way across gate pins (in other words be sure that the pins onthe gate highlight yellow rather than remaining black.) Always test the connections this way to make sure the exact connection youintended was made. Signals can appear to be connected, but not really be making the connection. Sometimes, even a solid yellowline will turn out not to be connected to the pin. If this happens you may see X values where you expect 0 or 1. Use the ? tool tocheck that the pin and wire have the same value.
    • Adjusting Wiring: You can adjust line segments within the connection path by clicking and dragginganywhere but on a corner.
    • Deleting wire segments or entire wire routes: If you want to delete only a portion of a signal line, use the “zap” tool. It looks like a lightning bolt. When the zap toolis selected, it will remove a line segment that it touches, up tothe nearest intersection, device pin, or segment join point. Selecting a signal and then using the delete key causes the entiresignal route to be removed.
  • Naming things: You can use the text cursor (the letter “A” on the tool palette at the top of the display) to name components,signals, and pins on your circuit. Select the “A” and then your mouse turns into a pencil. Move the pencil to the item you want toname and select the item. Devices have automatically generated names that you can modify by selecting them. Signals will bring upa small box for naming them when you select them while using the “A”. The auto-generated name will start with SIG. To check that thething you have named is really what you intended, select the object (signal or device). The name will highlight along with the selectedobject if it is correctly named. Signal and device names appear in pink, whereas expository text will appear black.
  • Simulation values:(0, 1, X, Z, or C) During simulation, a value of “X” denotes a state which cannot be determined. A value of“Z” denotes a high-impedance state. To turn simulation on, click on the “running man” icon in the tool bar, (he is to the right of the“speed” slider.) If you click on a switch to set a value, and simulation is not turned on, a pop-up box will appear asking if youwant to start simulation. Say yes, of course. A value of “C” denotes “Conflict” and means that DesignWorks cannot determine theproper value for a signal because it has been connected to two sources that are independent of each other; for instance connectingpower to ground. This error often occurs when you have named a signal in one circuit the same as a signal in another circuit inthe same file. DesignWorks interprets that to mean that the two signal wires are connected to each other. If that isn't what youintended, change the name of one of them.
  • Showing all values: DesignWorks can display all the signal values in the circuit with small blue numbers. To turn this off, from the Simulation Menu, select "Show Values".
  • Printing: You can print directly from DesignWorks using the File->Print menu. In order to make sure that the design prints on a single page, you can use Drawing->Sheet Size Wizard.One of the panes in the wizard will allow you to select Single PrintedPage. You can also save an image file of your circuit using File->Export->Windows Meta File.

Tutorial:

We will construct a four-input multiplexor and test its operation using switches and a hex keyboard. The finalversion is shown below and it corresponds to the illustration of a multiplexor in the text, on p. 61.

Four-input multiplexor

Example circuit to construct using Design Works for practice placing elements and wiring them.
  • Start DesignWorks Professional from the Program menu and select “new”, then “design”, then “Generic Simulation” from thefile menu.
  • To the right, you will see a parts palette. From the library selection drop-down list, choose “Simulation Gates”.
  • Double-click on the 3 input AND gate (AND-3). Your cursor will change into an AND gate. Place 4 of them vertically on thepaper by left clicking when the device is where you want it. To get out of “AND-3” mode, tap the space bar. You can move devicesaround, by clicking on them and dragging them to a new position. Pin 1 of all these gates will be the input lines, pin 2 will be thehigh order select line, and pin 3 will be the low order select line (or bit).
  • Attach inverters (“NOT”) to the appropriate input pins of each AND gate. Counting from top to bottom, place inverters on pins2 and 3 of the first AND, pin 2 of the second AND, and pin 3 of the third AND.
  • Now select the “OR-4” device and place it to the right of all the AND-3's.
  • Wire each of the outputs from the ANDs to the OR-4 circuit. (See Wiring in the reference section.)
  • Connect the signal lines going into pin 2 of each AND gate. The connection should be such that the signal line goes through anyapplicable inverter, after the connection has been made. Similarly, connect all the signal lines going into pin 3 of each AND gate.These will be the Select lines.
  • From the library selection drop-down list, choose “Simulation I/O”. Double click on the “Binary Probe” option and hook it up tothe output of your multiplexor. To orient the switch signal so that the switch connects to the output, use the arrow keys while placingthe component. Notice that the binary probe shows an “X” in its display. Since the inputs to the circuit have not yet been defined,the output is “undetermined”.
  • Select the “Binary Switch” component and place two of them on your drawing. Hook one of them to each of the combined input signallines into the multiplexor. Those will be the “selector” lines. Select 4 more binary switches and hook them up to the multiplexorinput lines.
  • Naming components of your circuit will help you to remember their function. Select the writing tool from the tool palette andname the devices and signals. Name the input signals, A, B, C, and D, and the AND gates corresponding to the selection of each ofthose signals. Name your select lines and output.
  • Turn on one of the input lines at a time, and use the selectors to select that value.
  • Having to turn each binary switch on and off individually can be laborious. Replace the 4 input binary switches with a single HEXKeyboard. What values of the HEX are convenient for testing the circuit? Use binary probes on the outputs of the hex if you gettired of converting in your head to determine which signals are high.

Questions & Answers

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research.net
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Source:  OpenStax, Fundamentals of computer engineering. OpenStax CNX. Oct 17, 2007 Download for free at http://cnx.org/content/col10347/1.4
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