3.4 Schematic entry in orcad  (Page 2/2)

/home/jpfrantz/elec424/tutorial/sch/Elec424Tutorial.pdf

A small hint for moving around in OrCAD: use ‘ I ’ and ‘ O ’ to zoom in and out, respectively. ‘ C ’ will center the design at your cursor. ‘ R ’ will rotate a part. You can do these actions while in the middle of another action (e.g. while placing a part). You will also notice that each part has a value associated with it. You can change this by double-clicking the current value. In this manner you can give all your capacitors, resistors, etc. theappropriate values. When you are done, the first page of your schematics should look something like this.

Now we need to draw nets to make electrical connections between components. To do this, click the Place Wire icon and connect the components as shown in the attached schematics. Use the Place Bus and Place Bus Entry icons to place busses and bus connections (you don’t need to do this in these schematics).

When you are done, the first page of your schematics should look like this.

Now you need to add power and ground connections to some of the parts. OrCAD has several built-in symbols for power and ground. I like to use a symbol that explicitly names the nets, as shown in the picture below. I do this because many designs will have multiple power and ground nets. Explicitly naming them helpsprevent shorts and other errors. It also makes your schematics easier to read. Add power and ground to your schematics now.

Connecting pages and naming nets

Since some of these connections go to the PLD, we need to a way to connect the two schematic pages together. We can do this by using off-page connectors. To place these click the Place Off-Page Connector icon. Then select the connector called OFFPAGELEFT-L or OFFPAGELEFT-R , it doesn’t really matter which one, they are functionally the same. You can place this on your schematic just like a part and then connect to it with a net. Off-page connectors are linked by a commonname. For example, two off-page connectors on separate pages with the name CLK will be considered by OrCAD to be one net. To name a connector, just double click it to get a naming dialog box. Name your connectors now using the attached completed schematics as a guide.

Normal nets can also be named. This is extremely useful and can help tremendously in the layout process. I encourage you to use the Place Net Alias icon to name any important nets such as clocks, address and data bus lines, and other specific signals you are interested in. To name a net, first highlight the net you want to name and then click the icon, you will be given a dialog box to enter the name of the net. You can position the text anywhere you like. If youhave already attached an off-page connector to a net, then that net already has the same name as the connector. You don’t need to give the net an alias unless it will make your schematics more readable.

If you have any pins on parts that are left unconnected, use the Place No Connect icon to mark it in your schematics.

Now complete your schematics as shown in the attached reference.