LogicWorks tips

Disclaimer

• These excellent hints are shamelessly stolen from previous quarters of Alex Orailoglu's 140L course.

Display

• Use binary probes or hex displays. Make sure that all input pins on a hex display are connected to a signal (don't leave floating pins)

Input

• Use binary switches or hex keypads. When using hex keypads, make sure that you know which pins are the most significant and which are the least significant. Many errors occur when people get the pins backward.

Learning new parts

• If you are not sure what a part does, you should make a new file with only that part. Hook up binary switches to each of the input pins and binary probes to each of the output pins. Experiment and try to understand exactly how the input affects the output.

Getting rid of messy wiring.

• Use busses. Under the "Schematic" Menu item choose "New Breakout..." Describe the pins you want on your bus. If you want pins labeled A0, A1, A2, A3, A4, A5 you can just type A0..5 and LogicWorks will know what you mean. The bus will collapse many signals into one line (slightly thicker than a regular wire). To use the signals on the bus you will need to use another breakout. Make sure that the names on both breakouts match.
• Don't use wires at all. You can skip wiring altogether by labeling pins. If you label two pins the same thing, LogicWorks will treat them as if they are connected. This means that you need to be very careful to make sure that all of the names are spelled correctly. Also make sure that two signals that are supposed to be separate are not named the same thing. 0 and 1 are "reserved" names. If you name a pin 0, LogicWorks will connect that pin to ground (logic 0). If you name a pin 1, LogicWorks will connect that pin to +5V (logic 1). Also make sure that you name the end of the pin (the name should appear in pink on the schematic).

Debugging

• Examine the output of parts to see that it matches what you expect. There are 5 possible values for an output signal (0,1,X,C,Z) . 0 and 1 are logic values. X usually occurs when a part has floating inputs. For example, if you have a hex display and ground 3 inputs, but leave the fourth unconnected, it will display a value of X. C indicates a conflict. If you connect ground to a binary switch set to 1, the wire connecting them will have a logic value of 0. Unconnected input pins have a value of Z.
• If you find that an output is X or C, trace the source of that problem backwards through the circuit.

Creating new parts

1. Create the circuit that will be the inside of the new part
2. Use a "Port In" part for each of the input pins for the new device. Make sure they are all labeled. To label a "Port In" part, first place the part in the schematic, then click on the text button (the one that looks like the letter 'A'). Type the name of the port in the text box that appears next to the "Port In."
3. Use a "Port Out" for each of the output pins for the new device. Name each "Port Out" according to the steps described above.
4. Under the "File" menu item, choose "New." In the window that pops up choose "Device Symbol" and click on the button "OK." There should be a blank schematic on the screen. Alternatively, you can use File->Libraries->New Part.
5. Under the "Options" menu item choose "Subcircuit/Part Type..."
6. In the window that pops up, choose "Create a sub-circuit symbol and select an open circuit to attach to it."
7. Select the appropriate circuit from the window that pops up and click "OK"
8. Click, the "Done" button. The list of Ports should appear on the left side of the screen. If it does not, you may not have labelled them correctly. Start over from step 2.
9. Now you will create a symbol for your part. The easiest way to do this is to select "Auto Create symbol..." under the "Options" menu item.
10. Type the name of each of the ports in one of the text boxes in the window that pops up (left pins, right pins, etc.). I usually put all of the input pins in the "Left Pins" box and all of the output pins in the "Right Pins" box. If you want pins names A, B, C, D to appear on the left side of the part, type "A B C D" (no quotes) in the box "Left Pins." It is important that you type the name of every pin in the circuit and don't type any pin names that do not appear in the circuit. When you are done, click the "Generate Symbol" button.
11. Now save your part in an appropriate library. (File..Save). For this class, you should make your own library and save your parts in it.
12. Now you can place your part in another circuit. You probably want to test your part first though.