Introduction to FCE1

Transcription

1 Universität Duisburg-Essen PRACTICAL TRAINING TO THE LECTURE Introduction to FCE1 Introduction to computer-aided design with OrCAD Name: First Name: Tutor: Matriculation-Number: Group-Number: Date: Prof. Dr.Ing. Axel Hunger Dipl.-Ing. Joachim Zumbrägel Universität Duisburg-Essen Faculty of Engineering, Department Electrical Engineering and Information Technology Computer Engineering Copyright (C) Computer Engineering

2 1. Preface The introduction to the computer-aided design with OrCAD is supposed to explain the basic approach to the design, simulation and analysis of digital circuits. As a case study for this practical training we will look upon the development of a Dual-Aiken-Code transformer. During the Fundamentals of Computer Engineering 1 practice course we deal with the OrCAD design suite, which consists of several different applications. Here we focus our attention on three of them: CAPTURE, PSpice and PROBE. In order to create and edit circuits we will use the graphical circuit editor CAPTURE (previously known as SCHEMATICS). The program PSpice is used for the actual simulation. The results of that simulation can be graphically represented by means of the oscilloscope-program PROBE. The complete design and simulation of a circuit is accomplished in four steps: 1. Create the circuit using CAPTURE. 2. Define the analysis type (also done in CAPTURE). 3. Simulate the circuit with PSpice. 4. Analyze the results with PROBE. 2. CAPTURE We will be using OrCAD CAPTURE to create and edit our digital circuits. The first step is to start up the CAPTURE application by going to: START Programme OrCAD 16.0 OrCAD CAPTURE The window shown in Fig 2.0 appears. In this windows plase select OrcadPCP Designer PSpice. Fig. 2.0 Once CAPTURE is running you should have a blank CAPTURE session frame with grey background appearing on the screen. The design process in CAPTURE is project-oriented, meaning you must create a new project before editing and simulating a circuit. To create a new project, go to: File New Project as illustrated in Fig /11

3 Fig. 2.1 The New Project dialogue box in Fig. 2.2 will appear. Create your new project using the Analog or Mixed A/D option. Name your project Dual-aiken-code and give as Location the following path: [drive_letter]:\orcad_data\intro. Hint: Ask you tutor for the right [drive_letter]! Fig. 2.2 Press OK to confirm your entries. Another dialog box Create PSpice Project appears as shown in Fig Choose the Create a blank project option and click OK. 3/11

4 Fig. 2.3 Now the working area appears (Fig. 2.4). On the left side is the Project Manager window that provides a graphical display of a project s resources by grouping them into hierarchically structured folders. These resources include schematic folders, schematic pages, part libraries, parts and others. Within the project manager, you can expand or collapse the structure you see by double-clicking on a folder, or by clicking on the plus sign or minus sign to the left of a folder. With a Right-Click on any project resource, one can edit its properties. On the right side is the Schematic Page Editor window. Here you can create, edit and display circuits by placing parts, wires and buses. When you click on the Schematic Page Editor window, a tool palette (on the right side) appears. With its help you can draw and place everything you need to create a circuit. Table 2.1 provides further explanation on the tools you will need for your circuit design. Project Manager Window Schematic Page Window Tool Palette Project Design Root Folder Schematic Page Fig /11

5 Tool Name Description Select Part Wire Net Alias Bus Select objects. This is the normal mode. Select parts from a library for placement. Equivalent to the Part command on the Place menu. Draw wires. Press and hold the Shift key to draw non-orthogonal (not a multiple of 90 ) wires. Equivalent to the Wire command on the Place menu. Place aliases on wires and buses. Equivalent to the Net Alias command on the Place menu. Draw buses. Press the Shift key to draw non-orthogonal segments. Equivalent to the Bus command on the Place menu. Table 2.1 To place a circuit part first make sure you are on the Schematic Page Editor window. The tool palette should appear on your right. Press the Part button or go to the menu Place Part. The Place Part dialogue box pops out. All parts are organized in libraries. In order to add a certain part, one should consider adding the corresponding library beforehand. In our practice we will work with the following libraries: dig_prim.olb, 74ls.olb, 7400.olb, breakout.olb and source.olb. The library dig_prim.olb contains ideal parts, meaning that they do not have any propagation delay. In contrast the libraries 74ls and 7400 contain real parts, implying that they have propagation delay. To add a library, press the Add Library button in the Place Part dialogue box. The Browse File dialogue box that is displayed can be used to locate a library and add it to the Libraries. Fig. 2.5 illustrates the Place Part dialogue box before and after libraries have been added. The Part List displays all parts that belong to the selected library. Fig /11

6 If you know the name of the part you need, you can type it directly in the Part text box. You can use wildcard characters to constrain the list of parts, then click OK. Valid wildcard characters are an asterisk (*) to match multiple characters and a question mark (?) to match a single character. However, if you do not know the exact name you can search for the part in the Part List. Once you find the part you need to press OK and place it via Left-Click on the Schematic Page. To connect parts we use wires. You can access the place wire option by selecting the Wire icon from the Tool Palette. Click the left mouse button to start the wire. Move the mouse to draw the wire. Click the left mouse button if you want to place a vertex and change directions. Double-click to end the wire. When you are done placing wires, choose End Mode from the right mouse button pop-up menu, or press ESC. Wires can also be connected physically to one another. If you begin or end a wire from or to another wire, as in a T-intersection, Capture adds a junction and the wires are connected. When you place a wire, it is assigned a system-generated name, which you can replace with an alias or a different name in order to simply identify wires when a circuit is simulated. Once a wire acquires a valid name or alias, that name or alias defines the signals carried by the wire. To create a net alias, select a wire on the Schematic Page. From the Place menu, choose Net Alias... or Click the Net Alias tool from the tool palette. Type a name in the Alias text box and choose a color, rotation, and font for display in the Place Net Alias dialog box (Fig. 2.6). Click OK to finish. Place the defined alias on the desired wire. Fig. 2.6 A wire is not allowed to have more than one alias. Different wires are allowed to have the same alias though. That way the wires are connected (Fig 2.7). This method is especially advisable for complex circuits! = Fig /11

7 Every circuit needs an input signal in order to be simulated. In Capture, input signals are simulated by sources placed in the same way as parts. They are located in the library Source.olb. Various sources may be used, but in our practical training we will focus on two of them. DIGCLOCK (Fig.2.8) is a digital cycle source, which generates a periodical clock pulse. Via double Click you can access the properties of this part or directly edit the attributes displayed around it. STIM1 (Fig. 2.9) is a digital signal source for 1 Bit. In its Property Editor we can define the desired signal pattern. Fig. 2.8 Fig. 2.9 Fig displays a sample input for the STIM1 properties. COMMAND1 initiates the signal with logical value of 0 at 0s. The entry in COMMAND2 defines a milestone at 100ns which switches the logical value of the signal to 1. Likewise COMMAND3 sets the signal to logical 0 at 300ns and again at 400ns COMMAND4 drives it to 1 until the end of the simulation (because no further commands were entered). You can observe the timing diagram of the sample input on Fig Fig Fig Simulation with PSPICE A/D Once the circuit has been created we can proceed with its simulation. The first step is to make sure that the circuit we want to simulate is located in a Schematic Page under the Root Folder, as shown in Fig Furthermore, all project changes must be saved before we carry on. Next create a new simulation profile by navigating to PSpice New Simulation Profile. The New Simulation window should pop out. In the field Name you should type the name of your simulation. From the drop down menu Inherit From, select none then click on Create. 7/11

8 The Simulation Settings dialogue box appears (Fig. 3.1). In the Analysis Type drop down menu, located in the Analysis tab, select Time Domain (Transient). The Run to time text field represents the duration of our simulation. Click OK to confirm your simulation profile settings. To run the actual simulation navigate to PSpice Run. After PSpice A/D completes the simulation, the graphical waveform analyzer starts automatically. A blank Probe window should appear. In order to observe the behavior of a desired signal during simulation, we must apply markers. We want to look at the voltage changes, which represent ones and zeroes (high and low voltage). For that purpose we choose to apply voltage markers by navigating to PSpice Markers Voltage Level. Place a voltage marker on a wire from which you want to observe a signal. This will yield to a plot of that signal in the Probe window as shown in Fig Fig /11

9 Fig Case Study: Dual-Aiken-Code transformer Your task now is to create and simulate a Dual-Aiken-Code Transformer circuit. The transformation of the Dual-Code into the Aiken-Code requires a digital circuitry, which is valid for the following truth-table: Decimal Binary-Code Aiken-Code number D C B A Z Y X W Table 4.1: Dual-Code to Aiken-Code The following equations are extracted from Table 4.1 and represent the output of the Dual-Aiken- Code transformer: W = A B C D + A B C D + A B C D + A BC D + A B C D X = A B C D + A B C D + A B C D + A B C D + A B C D Y = A B C D + A BC D + A BC D + A B C D + A B C D Z = A B C D + A BC D + A BC D + A B C D + A B C D 9/11

10 These equations could be minimized with the help of KV-maps. Adding Don t-care states will facilitate this process. W = A X = D + B C + A B C Y = D + BC + A C = D + C Z = D + BC + A C = D + C ( B + A) ( A + B) Fig. 4.2 illustrates the resulting circuit diagram of the Dual-Aiken-Code Transformer and Fig. 4.3 shows the simulation results. Fig /11

11 Fig /11