Sheet Symbol

Modified by Jason Howie on Feb 20, 2015
Contents

Parent page: Schematic Objects

A placed Sheet Symbol.

Summary

A sheet symbol is an electrical design primitive. It is used to represent a sub-sheet in a multi-sheet hierarchical design. Sheet symbols include sheet entry symbols, which provide a connection point for signals between the parent and child sheets in a hierarchical design, similar to the way that Ports provide connections between sheets in a flat-sheet design.

Availability

Sheet Symbols are available for placement in the Schematic Editor only, by clicking Home | Circuit Elements |  from the main menus.

Placement

After launching the command, the cursor will change to a cross-hair and you will enter sheet symbol placement mode. Placement is made by performing the following sequence of actions:

  1. Click or press Enter to anchor the first corner of the sheet symbol.
  2. Move the cursor to adjust the size of the sheet symbol and click or press Enter to complete placement.
  3. Continue placing further sheet symbols, or right-click or press Esc to exit placement mode.

Additional actions that can be performed during placement – while the sheet symbol is still floating on the cursor, and before its first corner is anchored – are:

  • Press the Tab key to access an associated properties dialog, from where properties for the sheet symbol can be changed on-the-fly.
  • Press the Alt key to constrain the direction of movement to the horizontal or vertical axis, depending on the initial direction of movement.
  • Press the Spacebar to rotate the sheet symbol anti-clockwise or Shift+Spacebar for clockwise rotation. Rotation is in steps of 90°.
  • Press the X or Y keys to mirror the sheet symbol along the X-axis or Y-axis respectively.

While attributes can be modified during placement (Tab to bring up associated properties dialog), bear in mind that these will become the default settings for further placement.

Graphical Editing

This method of editing allows you to select a placed sheet symbol object directly in the workspace and change its size, shape or location, graphically.

When a sheet symbol object is selected, the following editing handles are available:

A selected Sheet Symbol.

  • Click and drag A to resize the sheet symbol in the vertical and horizontal directions simultaneously.
  • Click and drag B to resize the sheet symbol in the vertical and horizontal directions separately.
  • Click anywhere on the sheet symbol – away from editing handles – and drag to reposition it. While dragging, the sheet symbol can be rotated (Spacebar/Shift+Spacebar) or mirrored (X or Y keys to mirror along the X-axis or Y-axis respectively).
Resizing the sheet symbol will not affect the absolute positions of any defined sheet entries within.

The sheet symbol's Designator and Filename text fields can only be adjusted with respect to their size by changing the size of the font used (accessed through the Sheet Symbol Designator and Sheet Symbol File Name dialogs, respectively). As such, editing handles are not available when either of these objects are selected:

Selected Designator and Filename for a sheet symbol.

  • Click anywhere inside the dashed box and drag to reposition the text object as required. While dragging, the text can be rotated (Spacebar/Shift+Spacebar) or mirrored (X or Y keys to mirror along the X-axis or Y-axis respectively).
  • The text for an object can be edited in-place by:
    1. Single-clicking the designator or filename text to select it.
    2. Single-clicking again (or pressing the Enter key) to enter the in-place editing mode. Sufficient time between each click should be given to ensure the software does not interpret the two single-clicks as one double-click (which would open the associated properties dialog).
    3. To finish editing in-place text, press the Enter key, or use the mouse to click away from the text object.

An object that has its Locked property enabled cannot be selected or graphically edited. Double click on the locked object directly and disable the Locked property, to graphically edit the object.

Non-Graphical Editing

The following methods of non-graphical editing are available:

Via an Associated Properties Dialog

Dialog page: Sheet Symbol

This method of editing uses the Sheet Symbol dialog to modify the properties of a sheet symbol object.

The Sheet Symbol dialog.

The dialog can be accessed during placement by pressing the Tab key.

After placement, the dialog can be accessed in one of the following ways:

  • Double-clicking on the placed sheet symbol object.
  • Placing the cursor over the sheet symbol object, right-clicking and choosing Properties from the context menu.

The sheet symbol Designator and Filename text fields can be formatted independently of the sheet symbol itself. The corresponding properties dialogs for each - the Sheet Symbol Designator and Sheet Symbol File Name dialogs respectively - can be accessed using the after-placement methods described above (replacing sheet symbol with the relevant object whose properties you wish to view/modify).

The Sheet Symbol Designator and Sheet Symbol File Name dialogs.

The Filename property of the sheet symbol, set on the Properties tab of the Sheet Symbol dialog (or through the Sheet Symbol File Name dialog), must be set to the file name of the schematic sheet that the symbol represents.

Via an Inspector Panel

Panel pages: SCH Inspector, SCHLIB Inspector

An Inspector panel enables the designer to interrogate and edit the properties of one or more design objects in the active document. Used in conjunction with the Find Similar Objects dialog, the panel can be used to make changes to multiple objects of the same kind, from one convenient location.

Sheet Symbol Actions

Right-clicking over a placed sheet symbol will pop-up a context-sensitive menu, from which the following commands are available (on the Sheet Symbol Actions sub-menu) that act on that sheet symbol (or all currently selected sheet symbols, where applicable):

  • Open SubSheet "<SheetName.SchDoc>" - use this command to access the child sheet referenced by the symbol, which will be opened (if not already) and made the active document in the main design window.
  • Create Sheet From Sheet Symbol - use this command to create a new schematic document from the sheet symbol and add ports to that document corresponding to each of the sheet entries on the symbol. In this way, you can automatically create the sub-sheets for a multi-sheet schematic design, based on the sheet symbols you have created and placed on the top sheet.
The schematic document that is created is named using the entry in the sheet symbol's Filename field. You can either enter the intended name for the document in this field before launching the command, complete with extension (i.e. DocumentName.SchDoc), or leave the name blank and enter the name when saving the generated document at a later stage.
Care should be taken when creating a sheet from a sheet symbol and a sheet with that filename already exists. A new sheet with the same filename will be created. The duplication can be resolved when saving, by either saving the new sheet with a different name, or overwriting the existing sheet if required.
  • Rename Child Sheet - use this command to quickly rename the child schematic sheet referenced by the sheet symbol. The Rename Child Sheet dialog will appear, with which to specify the new name for the document as required, as well as the scope of the renaming action.
  • Synchronize Sheet Entries and Ports - use this command to synchronize the sheet entries and sub-sheet ports for the sheet symbol. The Synchronize Ports To Sheet Entries dialog will appear. Use this dialog to ensure that all sheet entries on the sheet symbol are matched to ports on the referenced child sheet below, both in terms of name and I/O Type.
  • Flip Sheet Symbol Along X - use this command to flip the sheet symbol along the X-axis. The sheet entries associated with the symbol will essentially be swapped to the opposite side of the symbol (in the horizontal plane) - those on the left will be repositioned on the right and vice-versa.

Example of flipping a sheet symbol along the X-axis.

If multiple sheet symbols are currently selected, the command will appear as Flip Selected Sheet Symbols Along X. When flipping multiple selected sheet symbols, the symbols will be flipped about an imaginary vertical line which is located mid-way between the bounding extents of the symbols in the selection.
  • Flip Sheet Symbol Along Y - use this command to flip the sheet symbol along the Y-axis. The sheet entries associated with the symbol will essentially be swapped to the opposite side of the symbol (in the vertical plane) - those at the top will be repositioned at the bottom and vice-versa.

Example of flipping a sheet symbol along the Y-axis.

If multiple sheet symbols are currently selected, the command will appear as Flip Selected Sheet Symbols Along Y. When flipping multiple selected sheet symbols, the symbols will be flipped about an imaginary horizontal line which is located mid-way between the bounding extents of the symbols in the selection.
  • Toggle All Sheet Entries IO Type in Sheet Symbol - use this command to toggle the I/O Type for all sheet entries in the sheet symbol, simultaneously, and where applicable.

Example result of toggling sheet entry IO.

The actual change depends on the current I/O Type as follows:

  • Unspecified remains Unspecified
  • Output changes to Input
  • Input changes to Output
  • Bidirectional remains Bidirectional.

Notes

  1. If a group of sheet entries is pasted into a selected sheet symbol and those entries fall outside the current bounds of the symbol, it will automatically be resized to accommodate them.
  2. By using sheet symbol instantiation, multiple channels on the same sub-sheet can be referenced from a single sheet symbol. The syntax used involves the use of the Repeat keyword in the sheet symbol's Designator field and takes the form:

    Repeat(SheetSymbolDesignator, FirstInstance, LastInstance),

    where SheetSymbolDesignator is the base name for the sheet symbol and FirstInstance and LastInstance together define the number of channels to be instantiated. The FirstInstance parameter must start at a value of one (1) onwards.
  3. Multiple sub-sheets may be referenced by a single sheet symbol. Separate each filename by a semi-colon in the Filename field. With the effective use of off-sheet connectors placed on the sub-sheets, you can effectively spread a section of your design over multiple sheets, treated as though they were one giant (flat) sheet. Note however, that use of off-sheet connectors is only possible for sheets referenced by the same sheet symbol.

 

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