Bus / Register Tutorial

Description: A macro for a register is required for Lab 4, which utilizes a 4-bit bus for data input and a 4-bit bus for data output. This serves as a foundational example for creating similar macros for all components that utilize buses. To begin, a single click should be made at the desired starting point of the bus, followed by moving the mouse to the desired endpoint, right-clicking, and selecting "add bus terminal." It is important to remember that this process involves creating a macro, thus terminals are used. In the dialog box that appears, a name for the bus should be entered, the range defined, and the terminal set as either input or output. In this instance, the bus will be labeled "input." Since it must carry 4 bits of data, it will be designated as a 3:0 bus, with the terminal marker set to input. After selecting the tool, a single click on the bus is necessary, followed by clicking on all the pins intended for connection. Only one click on the bus is needed to avoid misconnecting to the wrong wire. If executed correctly, the wires emerging from the bus will be numbered 3, 2, 1, and 0. The same procedure applies to the output bus, ensuring that pins closest to the terminal are labeled identically to those on the input side to maintain data integrity. The schematic should now be complete. A macro can be created by accessing the hierarchy menu and selecting "create macro symbol from current sheet," entering a name for the macro, and clicking OK. This results in a macro available for use in the project. An example is provided that illustrates two linked registers. When connecting a bus to pads and buffers, the selection should be "add bus end" instead of "add bus terminal." It is noted that while this circuit may appear trivial, it effectively demonstrates the connection of components using buses and their integration with buffers and pads.

To design a 4-bit register utilizing buses in a schematic, the following steps can be elaborated. The register will consist of two main buses: an input bus and an output bus, each configured to handle 4 bits of data. The input bus, labeled as "input," will be defined as a 3:0 bus, allowing for the transmission of four distinct data lines. The output bus will mirror this configuration, ensuring that the data flow remains consistent across both buses.

The schematic layout will begin with the placement of the input bus, where the terminal is initiated at a chosen point, extending to the endpoint where connections will be made to the relevant pins of the register. Each pin should be clearly marked with its corresponding bit number to avoid confusion during data transfer. The output bus will follow a similar layout, ensuring that the connections are made in a corresponding manner to maintain the integrity of the data.

Once the buses are established, connections to the register's pins must be carefully executed. It is crucial to ensure that the pin labeling on both the input and output sides matches, as any discrepancies could lead to erroneous data interpretation. Following the completion of the bus connections, the entire schematic can be encapsulated into a macro for ease of use in future projects. This macro will streamline the process of integrating the register into larger circuit designs.

In summary, the creation of a 4-bit register with associated input and output buses serves as a foundational exercise in circuit design, demonstrating the essential principles of bus utilization and macro creation within electronic schematics. This process not only reinforces the practical application of registers but also enhances the understanding of data flow within digital circuits.Since you will be required to use buses and registers in lab 4, we will make a macro for a register that uses a 4bit bus for the data input and a 4-bit bus for the data output. You will need to make a similar macro for all your components that uses buses, so this will be a good jumping off point Single click at the point where you want the bus to

begin, then move your mouse where you want the bus to end, and right click, then select "add bus terminal" (remember that we are making a maco here so we use terminals) In the box that pops up, type a name for your bus, define the range, and set it to be input or output. In this case, we will just call it "input". Since it needs to carry 4 bits of data, we will make it a 3:0 bus, and we will set the terminal marker to input: After you have selected the tool, click on the bus you want to tap once, and then click on all the pins that you want to connect it to.

You only need to click on the bus ONCE, otherwise it will tap the wrong wire in the bus. If everything works out, the wires coming out of the bus should be numbered 3, 2, 1, and 0, as shown below: Do the same for the output bus. Be sure that the pins nearest the terminal are labeled in the same was as they are on the input side, otherwise your data will be flipped around.

Your schematic should now look like this: Make a macro for this now by going to the hierarchy menu and selecting "create macro symbol from current sheet". Then type a name for the macro and click OK. You should now have a macro to use in your project. Below is an example that shows two of these registers linked up. When we are connecting a bus to pads and buffers, instead of selecting "add bus terminal" for the bus end, just select "add bus end".

NOTE that this circuit is pointless, but demonstrates how to connect items using buses, and how to connect buses to bufs and pads.