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Set Up Design Parameters for PCB Layout Using Cadence Allegro

Picture of rice and pizza on a plate

Have you ever watched these cooking game shows where the contestants have to use unusual ingredients to compete with each other? Sometimes they get really odd combinations such as rice and pizza, or worse. Often when their shopping list is revealed to them, they will get this amazing look of disbelief on their faces as they try to figure out how to incorporate it all together into a workable meal.

I think that I’ve had that same look of disbelief before as I’ve opened up a new PCB design CAD system. Having to learn how to navigate around the user interface and make sense of all the different settings and preferences is very difficult when you are unfamiliar with the tool. All of these features and settings are important, but until you learn how to get the most out of them, they can be really intimidating.

Ease of Use in PCB Design Software 

At the end of the day, everyone wants to be able to do their job with ease and efficiency. Well, not so easy that it’s boring, but nobody wants the challenging part of their day to be figuring out how to use their tool. So many factors go into deciding which tool to use for your layout and design functions. And often these factors are outside of the hands of those who would even be using the tool in the first place. 

Ease of access, customization, and ease of interface should all be immediate factors for tool usage: can you even use the tool? But furthermore, learning a new software tool and adapting your processes is never ideal. Granted, with access to support documentation and training videos, certainly, anyone is going to be able to learn how to do what they need to do on any software. However, those are some precious several weeks or months of learning that could otherwise be spent creating something meaningful. 

Instead, I’d recommend looking for a tool that not only does everything you want it to do, but also exists within a structure of growth: if you, like any hopeful engineer I know, are looking to create something more, you’ll need a tool that will grow with you beyond your current parameters. 

For PCB design, I haven’t found a better tool than Cadence Allegro. It has the features and functionality to easily design the most challenging printed circuit boards that you can find. But in order to get the best out of the tools, you need to understand how the user interface and the design parameters all work together. To help you we are going to look at some of the basics of how to start with Cadence Allegro version 17.4 and explore some of these preferences and settings with you.

Moving Around in the Cadence Allegro User Interface

Using the board creation wizard in Cadence Allegro, you can create a very simple rectangular board outline complete with the basic parameters needed for the design. You can set up the layers, the units of measurement, plus much more. This is what we did in an earlier post about starting with Allegro, and that simple outline will serve us well here. With the board outline completed, the entire design session will look similar to the picture below. Because the different docked windows are moveable, however, you may see a lot of differences in how your application is laid out.

Screenshot of the entire Allegro session window

The Allegro PCB Designer session window with a board outline displayed

First of all, let’s start with a brief explanation of the different components of your Allegro design session:

  • Title bar: At the top of the session window is the title bar which identifies the application (Allegro), the current database, and the working directory.

  • Menu bar: Below the title is the menu bar with different pulldown menus. These pulldown menus provide you with all of the commands that Allegro is licensed for.

  • Icon toolbar: Below the pulldown menus is the icon toolbar. Icons represent the more common commands arranged in groups to make them easier for you to use. You can also reconfigure the icons to fit your personal needs by going to View > Windows.

  • Design window: This is the main design window that will display your PCB layout for placement, routing, and all other work.

  • Docked windows: Grouped around the design windows are the docked windows that can be configured with different commands and command groups. In the example above you can see for instance the “Design Workflow” pane to the left of the design window. This docked window provides you with sub-menus that follow a standard PCB layout workflow.

  • Status window: At the bottom of the design session, the status window displays your current cursor location, application mode, and DRC status among other data.

The docked windows allow you to precisely configure your design session. By going to View > Windows you can enable or disable the windows you want to display, and by using your mouse to drag corners or sides, you can resize the windows as needed. Additionally, in the upper right corner of each window are standard icons to fold, float, and close the window. To move the window around, select and hold the bar to the right of the window name with your cursor, and drag it to its desired location as shown in the picture below. The landing area for the window will turn blue showing you where the window will go.

Screenshot of Allegro’s fold-away windows being moved

Moving the fold-away windows around in Allegro PCB Designer

Now that we’ve set up the session window, let’s see how to navigate within the design window itself. The board outline that we created earlier should be displayed, and Allegro gives us a couple of different ways to manipulate the view.

As with many CAD programs the scroll wheel will zoom in and out, while holding the middle mouse button down will pan the display around as long as you’re at least partially zoomed in. You can also find different zoom controls from within the View pulldown menu, and those menu selections also have function keys assigned to them for your convenience. Another great navigational tool is the world view window. This shows you instantly where in the design window you are located at, and you can also use the world view window to zoom your design window in and out. Simply use your mouse to draw a rectangle within the world view window, and your design window will snap to the same point.

Setting Up the Allegro Design Parameters

Now that the board outline has been created and you understand how to navigate within the user interface better, let’s look at setting up some of the parameters for your design. Allegro gives you a lot of control over how your design displays and reacts to different control inputs, and we will only cover a fraction of what is available here in this article. Many of these settings can be found in the “Setup” and “Display” pulldown menus, but let’s look first at the “Design Workflow” window.

The Design Workflow window is intended to help you with a sequential set of commands that you would likely use during a design. Each category contains individual commands, and the categories follow a general design flow; database preparation leads to placement, and then constraints is followed by interconnect routing. The first category, however, is “Setup,” and that is where we will find many of the design parameters that can be adjusted.

In the Setup category, you will see the commands “Design Parameters,” “Grids,” and “Colors.” Each of these enables you to set up different areas of the design. Click on “Design Parameters” to bring up its editor window for example, and note the different tabs of settings that are available to you. In the “Design” tab, you can see the user units and drawing size that we set up earlier with the board creation wizard. You can find many different settings in each tab of the editor window, as well as the commands (Grids and Colors) in the workflow setup category. Close the Design Parameter Editor when you are done looking at the different setup options.

Screenshot of the user preferences editor in Allegro

Allegro PCB Designer’s User Preferences Editor

Next, go to Setup > User Preferences for more parameters to work with. Click on the little arrow to the left of the “Ui” category at the bottom of the categories list to expand it, and then scroll down and select “Input.” In the Input category preferences list to the right, hover your mouse over “designhdl_pan.” Just as in the picture above, you can see at the bottom of the editor window the following summary description:

“DesignHDL like roam/pan. With this option, Allegro panning behaves like many other applications. If set, mouse location is no longer fixed, and roam is in the same direction as the mouse movement.”

By changing the value of this preference when clicking on it with your mouse, you can change how Allegro will pan the main design window display when you use the middle mouse button. Go ahead, give it a try.

We have a host of online resources available at Cadence to support your learning about our commitment to upholding top-notch engineering. Check out our ebook version of The Hitchhiker's Guide to PCB Design and learn more about how you can improve your design process. 

If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts.