Adding Labels

Labeling identifies a net, bus, component, or pin by assigning a text string to it. Bus labels are required, and labeling all nets on the schematic makes debugging easier. Label all user-created macros.

Follow the conventions described in this section when you add labels.

Naming Conventions

FPGA names for nets, buses, components, and pins must follow these conventions.

• Use only A-Z, a-z, 0-9, “_,” and “-” in user-defined names. Do not include other characters in names.
  
  
• Use the Invert Sense convention. ViewDraw places a tilde (~) as the leading character of any signal name using this convention.
  
  
• Give names at least one non-numeric character.
  
  
• Restrict name length to no more than 256 characters.
  
  

Reserved Names

You cannot apply the physical names associated with every resource on every part to signals and symbols. These reserved names include CLBs, IOBs, clock buffers, BUFTs, oscillators, package pin names, CCLK, DP, GND, VCC, RT, PWRDN, and RST. Other examples include CLB names such as AA and AB, pin names such as P1 and P2, pad names such as PAD1 and PAD2, and primitive names such as TDO, BSCAN, M0, M1, M2, or STARTUP.

Net Names

ViewDraw and ViewSim fully specify hierarchical signal names; some examples follow.

• Unlabeled signals receive internal names generated automatically by ViewDraw. These names consist of a dollar sign, sheet number, “N” for net or bus, and a unique number assigned by ViewDraw for each net.
  
  
• ABC represents a labeled signal named ABC in the top-level drawing.
  
  
• $1I22\ABC represents a labeled signal named ABC underneath an unlabeled component called $1I22, where $1I22 is the symbol reference designator named with a dollar sign. This symbol reference designator derives from the sheet number (sheet 1), “I” for instance, and a unique instance number assigned by ViewDraw after each instance, in this case, “22.”
  
  
• $1N118 represents net $1N118, located on sheet 1 of the root-level drawing.
  
  
• $1I5\$1N118 represents net $1N118, a net in the
  top-level symbol $1I5. If the net exists in a schematic represented by a symbol on the design's top level, the default signal name reflects this hierarchy.
  
  

As these examples clearly show, putting more labels in your design makes it easier to locate signals for simulation.

Component Names

To give components more meaningful names than those issued by ViewDraw, use the Label field to name symbols, just as you would nets. The following lists some examples of symbol names.

• MYSYM - a component located at the top level of the drawing
  
  
• TOP\MYSYM - a component located one level below TOP
  
  

Components with or without user-assigned labels receive names in the following manner.

top-level_instance\instance

For example, $1I3\$1I5 represents a component (instance I5) located one level below symbol $1I3.

Bus Names

To ensure that bus signals process correctly, use the following naming conventions.

• Label all buses and all nets going into buses. For example, a bus labeled A[0:2] requires nets labeled A0, A1, and A2.
  
  
• Use EDIFNETO to expand bus notation. EDIFNETO expands bus and symbol pin names into individual signal or pin names. For example, a bus labeled DATA[0:3] converts into four nets labeled DATA0, DATA1, DATA2, and DATA3.
  
  

You must consistently apply the order of bus indices for a single bus. For example, do not connect busa[0:3] to busb[3:0] at another level of your schematic unless you are deliberately reversing the bus order.

See the following table for examples of legal bus names.

Table 3_1 Bus Name Examples

Adding a Label

Follow these steps to add a label to a net, bus, component, or pin.

1. Using the left mouse button, double click on the object you want to label. Alternatively, click the right mouse button on the object and select Properties.
   
   The Net Properties dialog box appears as shown in the “Net Properties Dialog Box” figure.
   
   
2. Type the name of the object in the Label field of the dialog box.
   
   

   Figure 3.12 Net Properties Dialog Box

3. Click on OK.
   
   The Net Properties dialog box closes, placing the label on the selected object.
   
   
4. To reposition the label, select the label only (not the object) with the left mouse button, then click and drag with the left mouse button to place the label.
   
   

You must label all buses and nets going into a bus. See the “Net Names” section, “Component Names” section, and “Bus Names” section earlier in this chapter for information on how to label these entities correctly.

Changing Net and Label Properties

To invoke the Net Properties dialog box, double-click on the net or bus. Use the Net Properties dialog to change some of the local properties of nets or buses, including the following.

• Net/Bus Label
  
  Under the Name tab, add or modify the label of net or bus in the Label field.
  
  
• Label Visibility and Sense
  
  Under the Name tab, you can use check boxes to define the label's visibility and sense. De-selecting the Visible box renders the label invisible. Selecting the Inverted box causes an overscore to appear over the signal name. This overscore becomes a leading tilde (~) when written into the EDIF netlist.
  
  
• Color and Style of the Net
  
  You can find these options under the Color, Etc. tab.
  
  
• Net Attributes and Visibility
  
  

Under the Attributes tab, you can add or modify net and bus attributes. To change the visibility of an attribute, select the attribute, then change the Visibility field. Click OK to save the change. See the “Adding Attributes” section of this chapter for more information.

Access other properties through the Label Properties dialog box. To invoke this dialog box, double click on the label (make sure the net or bus itself is not selected). In addition to the Label, Visibility, Color, and Sense parameters, you can modify the following.

• Text Size
  
  Under the Name tab, change the size of the text in the Size field.
  
  
• Text Origin
  
  Under the Color, Etc. tab, choose the location of text origin of this label.
  
  
• Label Color and Font
  
  

Under the Color, Etc. tab, choose the color and Font for this label.

To apply any changes made in the Net Properties or Label Properties dialog boxes, click on OK. To exit the dialog box without making schematic changes, click on Cancel.

You can set the default value of many of these properties from the Project Settings menu selection.