3.6 Starting layout in orcad  (Page 5/9)

When routing you will want to refresh the display occasionally to redraw the ratsnests. Now connect the resistor to the PLD. Since our traces on the top layer are already oriented horizontally, let’s place this vertical route on the bottom layer. When you begin the route, press ‘2’ to switch to the bottom layer. Since the resistor is a thru-hole part, there is no need for vias in this situation.

Route the trace to the top of the PLD. When you get near the top, you can press ‘ V ’ to place a via. Then you can switch to the top layer to complete the trace.

You now have your first complete route. You can begin to finish the other connections. Start by routing one component at a time. For example, you might route the TIL311 next, as is shown above. It is also important to route critical signals first, such as clocks and resets. Remember that you can zoom and pan during operations such as routing. The DRC routing box will move with you. With the current DRC settings, you may sometimes see circles around your traces if you get too close to another net or pad. If this happens, then Layout is warning you that you are making a spacing violation with your route. You will need to fix it. I would also suggest that you browse the shortcut keys in the help to see which shortcuts will be useful during routing. When you are done routing, your design may look something like this.

Congratulations! All the really hard work is done. Now there are just a few remaining steps to complete your board for submission to a board shop for fabrication.

Performing ecos&Back annotation

What if you wanted to make some changes to your design while you were in Layout? OrCAD provides the means for this through ECOs (Engineering Change Order) and back annotation. An ECO is used when changes are made in schematics (perhaps you added some more circuitry or changed some connections). Back annotation is used for changes made during Layout.

When you saved your file, Layout reminded you to back annotate. This was because we added the mounting holes to our design, and OrCAD wants to export those back to schematics. Even though it is not entirely necessary right at this moment, let’s step through the process so you know how it works. On the menu click Auto-->Back Annotate . OrCAD will create a swap file called Elec424Tutorial.swp in your board directory. It is safe to overwrite your existing board file with the new one. Look at the swap file in Notepad. You will see several sections. One thing that Layout does is update part and net properties (such as its coordinates) in Capture. If new components were added, then you would also see those changes. Now let’s import this file into Capture. Start Capture and highlight your dsn file. Select Tools-->Back Annotate… You can leave the Scope and Mode settings untouched. Use the Browse button to find your swap file. Click OK to start the update. Occasionally, when you add components like mounting holes, you will get an error during back annotation. This is usually safe to ignore.