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Design Annotation is the systematic and methodical process for ensuring that each component in the design can be individually identified by means of a unique designator. While Altium Designer is able to maintain the identity of components using Globally Unique IDs (GUIDs), most designers will historically use the component's designator as the primary means of referencing the component across the Schematic (logical) and PCB (physical) domains, as well as in outputs such as the Bill of Materials (BOM).

There are three approaches to annotating a design. The choice of Annotation Tool depends on a number of factors including the type of design, personal preference, and company policy and procedures:

Schematic Level Annotation

Schematic Level Annotation uses a purely logical view of the design to determine component designators. It is most useful for simple designs that do not use Device Sheets but because it allows the order of processing to be specified as well as the option to complete existing packages for multi-part components, it is also a pre-requisite to Board Level Annotation.

In summary, use Schematic Level Annotation to:

• Package Multi-Part Components
• Annotate components based on their position in the Schematic Design
• Annotate Multi-Channel designs using the default naming scheme as specified in the Project Options
• Prepare a design for additional annotation.

PCB Annotation

PCB Annotation uses the physical location of components on the PCB to determine their designation.  This allows positional information to be effectively encoded into a component's designator and can be very helpful when debugging an assembled PCB.

In summary, use PCB Annotation to:

• Annotate components based on their position on the board in the PCB Design.

Board Level Annotation

Board Level Annotation provides a mapping between designators used in the Schematic (Logical) Design and their real world counterparts on the PCB (Physical) Design. While Board Level Annotation can be used in any design, it is especially useful for multi-channel designs and / or designs that incorporate Device Sheets where the designators cannot be edited on the Device Sheet itself. In this way, the entire design can be re-annotated without actually modifying the original Device Sheet(s).
Board Level Annotation resolves any conflicting annotation problems that may occur due to duplicate designators across a project and stores its changes in an *.Annotation text file. It includes additional keywords for customizing naming schemes and allows them to be applied to all or only a select range of parts.
In summary, use Board Level Annotation to:

• Annotate the compiled components in Device Sheets
• Uniquely name all components across several channels using naming schemes which include positional annotation, global indexing, and other configurable options
• Manually name components

Schematic Annotation

The Annotate Schematics command systematically assigns designators to all or selected parts in selected sheets of a project and ensures that designators are unique and ordered based on their position. Annotation options can be configured to package multi-part components, set Index and Suffix options, Reset Schematic Designators including any duplicate designators and Back Annotate from PCB.

The Annotate Schematics command is accessible from the Tools » Annotate Schematics menu.

The Annotate dialog is launched from the Annotate Schematics command.

The Annotate dialog box is partitioned into two primary sides:

1. The left side is for configuring the Order of Processing, setting Matching Options for multi-part components, and setting the scope of annotation; including setting an Index and adding a Suffix for designators per Schematic Sheet
2. The right side lists the proposed changes that will occur once the Accept button is clicked. It includes the Current and Proposed designators along with the option to lock (exclude) specific designators and / or sub-parts from annotation.

Order of Processing

Positional annotation is directed through the Order of Processing control. Four options are available to control how schematic documents will be scanned:

Specifying the order that components will be processed.

Matching Options

Matching components into multi-part packages.

When using multi-part packages, it is often desirable to pack as many parts into the minimum number of physical parts since this minimizes the overall BOM cost of the design. Primary considerations for annotating multi-part components are how those components will be matched and grouped together, and the criteria used for determine valid groupings.

Complete Existing Packages

In order for multi-part packing to be included as part of the annotation process, the Complete Existing Packages drop down must be set to something other than None.

• None - existing packages will not be completed and all new parts will be placed into new packages
• Per Sheet - existing packages will only include new parts from the same Schematic Sheet
• Whole Project - existing packages will include new parts from any of the Schematic Sheets in your project.

Locking parts to prevent packing changes. For non-homogeneous multi-part components,
check the Locked attribute to prevent sub-part changes during annotation.

Component Parameters

The Component Parameters list includes all parameters found within components in the current design.  If multi-part components share the same enabled parameters and a common value, then they will be packaged together (assuming the Complete Existing Packages option is not None).

The default settings in the Annotate dialog are to complete existing packages by Library Reference and Comment, however any combination of parameters can be selected by the designer.

Strictly

If the Strictly checkbox is enabled for a Component Parameter, all components must have that parameter to be matched into a package. Components that do not have this parameter are annotated as individual components and are not packaged.

The following example illustrates how these options combine to give a specific result:

Consider a design with 8 OR Gates and 8 resistors (see the image below). The OR gates contain a parameter called QuadOrGate, with one group of 4 OR gates having the parameter value Package1 and the other group of 4 OR Gates having the parameter value Package2. The resistors have no such parameter. Enabling the checkbox for QuadOrGate in the Component Parameter control will ensure that this parameter is used to control how components are packaged; in this case, the Strictly check box is not enabled.
After launching Tools » Annotate Schematics, parts with the parameter  QuadOrGate = Package1 will be packaged into the same physical component and those that have the parameter QuadOrGate = Package2 will be packaged together separately. Any remaining components which do not have the QuadOrGate parameter will be packaged together. In this case, the resistors are packaged together as their common attribute is that they do not contain the QuadOrGate parameter.

Example of packaged components when the Strictly option is unchecked.

If the same design is annotated but this time with the Strictly option checked, only those components that have the QuadOrGate parameter will be packed. So in this case, the OR gates will be packed but the resistors left unpacked. So while the Strictly option provides extremely fine control over the packing process, most situations will have it left unchecked.

Example of packaged components when the Strictly option is checked.

Schematic Sheets to Annotate

A high degree of control is provided over which Schematic sheets and components will be effected by annotation, and the specifics of how those changes will be calculated.

Specifying the scope of annotation.

• A tick in the checkbox to the left of the Schematic Sheet indicates that it will be processed as part of the annotation command.
• The scope of annotation is determined by the Annotation Scope drop down list and can be expanded to include the entire schematic sheet, or limited to (un)selected components. Using the Ignore Selected Parts or Only Selected Parts options requires that the components were selected in the design prior to running the Annotation command.
• Configure the order in which the Schematic Sheets are to be annotated using the Order field. Type a value directly into the field or use the arrows which appear once you click in the field to set the desired value.
• If the Designator Index Control checkbox is ticked, the designator value will begin from the Start Index value. The Start Index has no effect if the Designator Index Control checkbox is not ticked.
• An additional suffix can be added to the end of each designator by specifying a string / value in the associated Suffix column. Avoid using single character suffixes such as 'A' or '1' as these can be easily confused with sub-parts and / or other designator values.

Proposed Change List

Clicking the Update Changes List button will update the Proposed Change List so that all designator changes can be reviewed prior to being applied. Only designators that have not previously been set (i.e. R?, C?, etc) will be effected by the changes so if the intention is to update all designators in the design, they should be first reset by pressing the Reset All button.

Resetting designators prior to applying the annotation settings.

The Proposed Change List lists all designators for the parts contained within the sheets selected for annotation. For each entry, details of the Current and Proposed Designator values are included along with the component's Sub (part) and the source Location of Part.
Checking the box adjacent to a Designator will lock that specific designator from any changes. Similarly, checking the Sub box will prevent that specific multi-part component from being updated. This option can be used as an alternative to setting the Lock attribute in the component's properties dialog.

After reviewing the list of proposed changes, clicking the Accept Changes (Create ECO) button will launch the Engineering Change Order dialog and a final layer of validation and reporting can be applied.  Once the ECO is executed, the annotation changes will be applied to the design.

Additional Schematic Annotation Commands

The Tools menu contains a number of targeted Schematic Annotation commands. The first item in the group, Annotate Schematic, has already been discussed.

Various available annotation commands.

Reset Schematic Designators

If large portions of content have been cut and pasted from different sources into a new design, it may be necessary to reset all designators. Because this command uses settings taken from the Annotate dialog, it will be applied to items previously set within that dialog.  For instance, if all Schematic Sheets to Annotate were previously checked, then the Reset Schematic Designator command will apply to the entire project, whether the sheets are currently opened in the editor or not. If only a few Schematic Sheets to Annotate were previously checked then the Reset Schematic Designator command will only affect those sheets.

Any designators with a locked status are not reset or changed in any way.

Reset Duplicate Schematic Designators 

When duplicating portions of a design, the newly copied components will still hold the same designator values as those that they were copied from.  The Reset Duplicate Schematic Designators command provides a fast way to reset duplicate designators to '?'. Once again, because this command uses settings taken from the Annotate dialog, it will be applied to items previously set within that dialog.  For instance, if all Schematic Sheets to Annotate were previously checked, then the Reset Duplicate Schematic Designator command will apply to the entire project, whether the sheets are currently opened in the editor or not. If only a few Schematic Sheets to Annotate were previously checked then the Reset Schematic Designator command will only affect those sheets.

Any designators with a locked status are not reset or changed in any way.

Annotate Schematics Quietly

The Annotate Schematics Quietly command makes it possible to apply all of the previous settings of the Annotate dialog without needing to reopen the main dialog.  So if the design is going through a rapid phase of development and the designer wants to quickly annotate prior to compiling the design, the Annotate Schematics Quietly command is the quickest way to do this.

Force Annotate All Schematics

Running the Force Annotate All Schematics command is equivalent to running the Reset Schematic Designators command followed immediately by the Annotate Schematics Quietly command. Consequently, the Force Annotate All Schematics uses settings that were previously set within the Annotate dialog when determining which components and sheets can be updated.

After launching this command, a request for confirmation will appear that details the number of designators that will be updated if accepted.

Back Annotate Schematics

Prior to the introduction of Altium's Design Compiler and Synchronizer, annotation changes were historically passed form the Schematic to the PCB via a netlist (*.net) file.  Annotation changes that needed to propagate in the reverse direction - from PCB to Schematic - were handled via a Back Annotation process. This process uses a Was-Is (*.WAS) file or Engineering Change Order (*.ECO) file to direct the changes to be applied to schematic designators.

The Back Annotate Schematics command is largely superfluous since the Design Compiler and Synchronizer are far more effective tools for managing design synchronization (Design » Update to). But for legacy purposes and for designers who use alternate PCB layout tools (such as Specctra^®), the Back Annotate Schematics command remains available in Altium Designer's menu system.

Number Schematic Sheets

The Number Schematic Sheets does not alter component designators but rather Schematic Sheet Designators (numbers). Conceptually, it is therefore related to the general concept of design annotation.

Sheet and Document Numbering allows designers to take control over the sheet designation and store them as parameters within the respective schematic documents. Altium Designer's special string feature (=SheetNumber, =DocumentNumber, =SheetTotal) can then be used to expose these values on the sheet (in the sheet footer for example) as text objects.

Numbering Schematic Sheets.

The process of numbering sheets is as follows:

Auto Sheet Number

Click on the Auto Sheet Number drop down button to expose the sheet numbering options.

Auto Sheet Numbering Options.

The Select Numbering Scheme options are as follows:

• Display Order - The sheets are numbered in the order they are displayed
• Sheets Hierarchical Structure - Depth First: The sheets are numbered from the top level into each branch. The top level is numbered first and then the first branch under the top level is numbered completely, the second branch and so on.
• Sheets Hierarchical Structure - Breadth First: The sheets are numbered according to their level in the hierarchy. Top level is numbered first, all second levels are numbered next and so on.

The Select Numbering Method allows for Increasing or Decreasing sequential values to be selected.

Auto Document Number

Click on the Auto Document Number drop down button to expose the document numbering options.  They are essentially the same as the Auto Sheet Number options but with the addition of Prefix and Postfix values.

Auto Document Numbering Options.

The Parameters options are as follows:

• Prefix - choose a prefix to affix in front of your Document Number. Alpha (A, B, C, etc) numerical (1, 2, 3, etc) and non numerical (_,*,.,%, etc) prefixes are supported including combinations of all of them.
• Start - choose a numerical value to begin Document Numbering from.
• Postfix - choose a postfix to append to the Document Number. Alpha (A, B, C, etc) numerical (1, 2, 3, etc) and non numerical (_,*,.,%, etc) postfixes are supported including combinations of all of them.
• Step - choose a value to increment each Document Number by. For example, if the Start index is set to 1 and the Step value set to 100, the first Document Number will be 1 and the next Document Number will be 101 (Start + Step), the next one will be 201 and so on.

Update Sheet Count

Clicking on the Update Sheet Count button will simply tally up the number of sheets in the current project and place the result in the SheetTotal column. The sheet count will be the total number of sheets in the project regardless of the numbering scheme selected in either of the previous controls.

Move Up / Down

Use the Move Up or Move Down buttons to move a selected Schematic Document up or down respectively in the list. This is relevant when using the Display Order numbering scheme to specify Sheet or Document Numbers.

Custom Numbering / Naming

If an organization has a specific number or naming system that can't be automated through either the Auto Sheet Numbering or Auto Document Numbering commands, custom sheet names and numbers can be written directly into the SheetNumber or DocumentNumber fields.

Applying custom Sheet Numbers.

Schematic Sheet Numbering and Device Sheets

Sheet or Document Numbers cannot be configured for Device Sheets when they are read-only (default state) and will be cross hatched in the Sheet Numbering dialog to indicate they cannot be updated. When Device Sheets are set as editable, the cross hatching is removed and Sheet and Document Numbering can be configured as normal.

Device Sheets cannot be renumbered if they are set as read-only.

Board Level Annotation

Board Level Annotation is the process of annotating the compiled components (the physical view of your components) of your design through the Schematic Editor. Board Level Annotate allows you to either name your components based on a number of Naming Schemes, Back Annotate from PCB documents to the Compiled Documents or specify custom names. Board Level Annotation is also useful if you are implementing Device Sheets in your project since Board Level Annotation is the annotation of the Compiled Documents not the source document, which in the case of Device Sheets, is read-only by default.
Board Level Annotation gives you complete control over the annotation in your project with annotation settings saved in a *.Annotation text file, displayed under the Settings\Annotation Documents sub-folder in the Projects Panel. Altium Designer manages Annotation files automatically.
You can choose to name all of the components in your project, name selected components or name only those components which are undesignated.
To annotate the compiled components in your project through the Schematic Editor:

• Ensure that the components have been annotated at the Schematic Level so that the Schematic source data including packaged options for multi-part components is available as input for your Board Level Annotation
• Select Tools » Board Level Annotate (Ctrl+L) which brings up the Board Level Annotate dialog. The left hand side of the dialog is for filtering and setting the scope of annotation and the right hand side shows the proposed changes
• Note that the project is compiled every time you perform a Board Level Annotation to ensure the most current design and preferences are used.

The Board Level Annotate dialog is displayed with all of the Schematic Documents in your project.

Filter Options

The left hand side of the Board Level Annotate dialog allows you to control the scope of annotation at the Sheet, Channel and Part Level. The columns in the Filter Options control do not change.

Schematic Sheet

The Schematic Sheet column lists all of the Schematic Documents in your project. A Schematic Document may be listed more than once if your design includes multiple channels.

Channel Name

The Channel Name column lists all of the relevant channels in your design. If there are no channels in the design, this column will be populated with the Schematic Sheet name.

Enabled

Tick this check box to include the Schematic Sheet for a specific Channel in this Board Level Annotation. Uncheck the box to exclude this sheet from Board Level Annotation.

Annotation Scope

Choose from the following to set the scope for the parts to be annotated:

• All - All parts in the Schematic Sheet will be annotated
• Ignore Selected Parts - All parts except those selected will be annotated
• Only Selected Parts - Only the parts selected will be annotated

All On, All Off Buttons

When pressed, the All On button ticks the Enabled checkbox for all Schematic Sheets in the project, including them in annotation. The All Off button disables the Enabled checkbox for all Schematic Sheets in the project, excluding them from annotation.

Proposed Change List

The right hand side of the Board Level Annotate dialog allows you to view Schematic Source Components (highlighted in pink), view Calculated Design Data used in the current naming scheme whether this is the default names for compiled components or the applied naming scheme, (highlighted in green), apply a Naming Scheme and view the resultant PCB Component Instance.

Schematic Source Component

The Schematic Source Component section is made up of three columns:

• Hierarchy Path - the path of the Schematic Source, in the format Filename\Channel
• Prefix - the alphabetical prefix extracted from the Schematic Level Designator e.g if your Schematic Level Designator is R13, the Prefix is R.

• Local Index - the index you have specified following the alphabetical prefix, extracted from the Schematic Level Designator e.g if the Schematic Level Designator is R13, the Local Index is 13.

Calculated Design Data

Upon first opening the Board Level Annotate dialog, the Calculated Design Data section displays the Room Name column, which corresponds to the default Annotate Option selected.
Once you have performed a Board Level Annotation, the columns displayed in the Calculated Design Data represent the keywords selected in your naming scheme for annotation in your Annotate Options. These columns are updated dynamically based on your selection. For example, if you select your Naming Scheme to be $GlobalIndex.$SheetDesignator, the columns displayed will be Global Index and Sheet Designator.

Naming Scheme

Tick the check box to enable the Naming Scheme for this component. Uncheck the box to disable the Naming Scheme for this component. Note that when this field is unchecked, the PCB Component Instance column can be edited so you can specify a custom designator for your component.

PCB Component Instance

The PCB Component Instance column displays the proposed designator. This field is dictated by either the Naming Scheme selected or a custom value which can only be specified when the Naming Scheme field is unchecked. The custom name can contain any combination of alphanumeric and non-alphanumeric characters.

Annotate Options

Annotate Options (accessed by clicking the Annotate Options button in the Board Level Annotation dialog) allows you to further customize your Annotation using either predefined or custom Naming Schemes.

The Board Level Annotation Options dialog.

Predefined Naming Schemes

To apply a predefined naming scheme:

• From the Board Level Annotation dialog, click the Annotate Options button to open the Board Level Annotation Options dialog.
• Select a predefined Naming Scheme from the drop down list
• Once you have selected a naming scheme, customize any other options such as Global Index Options or Room Name Options and click OK. Customization options vary between predefined naming schemes.
• Notice that the Calculated Design Data columns are updated to reflect the keywords used in your Naming Scheme.

Custom Naming Schemes

To apply a custom naming scheme:

• From the Board Level Annotation dialog, click the Annotate Options button to open the Board Level Annotation Options dialog.
• Define your own Naming Scheme using valid keywords by typing directly into the Naming Schemes field. You can select any combination of valid keywords in any order to define your own naming scheme. You can use any non-alphanumeric character in your Naming Scheme to separate keywords e.g.
  _ * . @ etc.
• Choose from the keywords tabulated below:

Keyword	Definition
$RoomName	Name of the associated Room, as determined by the style chosen in the Room Name Options.
$ComponentPrefix	Component Logical Designator prefix (e.g. U for U1).
$ComponentIndex	Component Logical Designator index (e.g. 1 for U1).
$ChannelPrefix	Logical Sheet Symbol Designator.
$ChannelIndex	Index you have specified to distinguish between different channels.
$ChannelAlpha	Channel Index expressed as an alpha character. This format is only useful if your design contains less than 26 channels in total, or if you are using a hierarchical designator format.
$SheetDesignator	Designator assigned to the Sheet Symbol.
$SheetNumber	The Sheet Number assigned to the Sheet. If Compiled Sheets have been annotated, this information will be used.
$DocumentNumber	The Document Number specified in Document Options.
$GlobalIndex	User defined index. You can specify the order, Start Index and/or a suffix in the Global Index Options for each schematic document. These options are displayed in the Board Level Annotation Options dialog. Global Index is calculated for all undesignated components. If you add new components after you have performed a Board Level Annotation, these components will be annotated with a new Global Index and the existing components will retain their Global Index. To recalculate the Global Index for all components, Reset All first.

Alternatively, if you wish to specify a custom name for all or a particular component, uncheck the Apply box under Naming Scheme column to disable the Naming Scheme for selected components and edit the PCB Component Instance column.

Annotate

To complete Board Level Annotation:

• Click on the Annotate drop down and choose whether you want to Annotate Undesignated, Annotate All or Annotate Selected
• The U1 column is updated with the designator to be annotated to each component
• Click the Accept Changes (Create ECO) button. The Engineering Change Order dialog appears, allowing you to validate, report and execute the ECO.
• Click Execute Changes button and then the Close button to execute Board Level Annotation
• Click the Close button on the Board Level Annotate dialog
  Your *.Annotation file will be updated and you can view your Board Level Annotation in your Compiled Documents. To complete Board Level Annotation, synchronize your Schematic Documents with your PCB Documents by selecting Update PCB Document Filename from the Design menu.

Reset All

Use the Reset All button in the Board Level Annotation dialog to reset all of the designators back to the default names for Compiled Components. These default names are configured in the Project Options dialog accessed through the Project menu. Once components have been reset, The Prefix column will display a component icon with a question mark to show that the component is now undesignated.

Back Annotation

Click the Back Annotate button in the Board Level Annotation dialog to synchronize changes from your PCB design to the Compiled Documents in the Schematic Editor. After clicking the Back Annotate button, the Choose WAS-IS File for Back-Annotation from PCB dialog appears. Select your file for Back Annotation.
Back Annotation for Board Level Annotation performs the same way as it does for Schematic Level Annotation.

Annotating Compiled Sheets

You can annotate your compiled sheets using the Tools » Annotate Compiled Sheets command. This function enables you to uniquely name the Compiled Documents (the physical representation of your design). These values are mapped to the SheetNumber special string and are stored in the *.Annotation file. This file is displayed under Settings\Annotation Documents sub-folder so that annotation information is remembered when you close your project. Annotate Compiled Sheets command treats Device Sheets like other sheets in your project and annotates them according to your Annotation options.

The Annotate Compiled Sheets dialog.

Annotating Compiled Sheet Options

Click on the Annotate Sheet drop down combo to choose your Compiled Sheet Annotation Options.

Numbering Order

• Display Order: The sheets are annotated in the order they are displayed
• Sheets Hierarchical Structure - Depth First: The sheets are annotated from the top level into each branch. The top level is annotated first and then the first branch under the top level is annotated completely, the second branch and so on

The Navigator view of your project shows the compiled (physical) representation of your sheets. When you annotate the sheets 'depth first,' you annotate each branch of the hierarchical structure at a time.

• Sheets Hierarchical Structure - Breadth First: The sheets are annotated according to their level in the hierarchy. Top level is annotated first, all second levels are annotated next and so on.

The Navigator view of your project shows the compiled (physical) representation of your sheets. When you annotate the sheets breadth first', you annotate the sheets based on their position in the hierarchy. For example, the top sheet, EqualizerTop.SchDoc is annotated first and then all of the second level sheets are annotated next.

Numbering Method

Choose to Increase or Decrease the annotation of your compiled sheets based on the Numbering Order chosen.

Annotating Compiled Sheets

After selecting your options:

• Click the Annotate Sheet button, the Sheet Number field will be updated to match your selections
• Click OK to accept your changes.

Custom Annotation of your Compiled Sheets

You can create custom names for your Compiled Sheets by typing directly into the Sheet Number field. You can use any combination of alphanumeric or non-alphanumeric characters. After entering your custom names, click OK to implement your custom annotation.

Using Compiled Sheet Annotation in your Board Level Annotation

Once you have annotated your Compiled Sheets, use the $SheetNumber keyword in your naming scheme when performing a Board Level Annotation to use this information in your annotation. If you have not annotated your compiled sheets, the Schematic Sheet numbering (Tools » Number Schematic Sheets) information will be used.

Using Compiled Sheet Annotation in your Project

Once you have annotated your compiled sheets, you can place the SheetNumber special string in your project to reference this information.

• Ensure that you have Convert Special Strings enabled in DXP » Preferences » Schematic » Graphical Editing
• Place a special string where the value =SheetNumber to use your Compiled Sheet Annotation values. You can use Special Strings in values of Parameter Properties, Text Strings, Net Labels etc.

Board Level Annotation and Device Sheets

Device Sheets are portable and can be re-used between designs. In most cases, the names of the components in Device Sheets are limited to the scope of that sheet, and require Board Level Annotation in order to be incorporated into the design in which they are placed.
Board Level Annotation is relevant to Device Sheets due to the fact that different Device Sheets included in one project can contain duplicate designators, resulting in compilation errors. Board Level Annotation can resolve any conflicting naming with the changes saved to a *.Annotation file displayed under the Settings\Annotation Documents sub-folder.

Default Names for Compiled Components

Default Names are required to be able to distinguish between the different instances of the physical representations of components. These default names are displayed in your Compiled Documents and are used if you have not performed a Board Level Annotation to annotate your compiled (physical) components. When you first launch the Board Level Annotate dialog, the default names are populated in the PCB Component Instance column.
Default naming of compiled components is also applicable for Multi-Channel designs which reference the same sheet in a project multiple times. This is done by either placing multiple sheet symbols which reference the same sheet in the Schematic Document or by including the Repeat keyword in the designator of a sheet symbol, to instantiate a sheet multiple times.

While this makes it easy to repeat circuitry, it also presents a challenge in terms of annotation. In a Multi-Channel design there can only be one logical instance of each component with its own unique designator, no matter how many "copies" of it exists on the PCB. The Multi-Channel tab of the Project Options dialog (Project » Project Options) ensures that each channel is uniquely annotated with a default name based on Room Naming Styles and Component Designator Format.

Multi-Channel Tab

Rooms are regions that assist in the placement and annotation of components in multi-channel designs. More specifically, a channel on the Schematic is an instance of a repeated sheet and on the PCB each channel is represented by a room. Once components have been assigned to a room, they move when the room is moved, allowing separate channels to be easily controlled and identified.

Rooms play an important role in channel designations ensuring unique names.

Logical designators are assigned to the components in the Schematic Editor View. Physical designators are assigned to the components when they are placed in the PCB design or when you have performed a Board Level Annotation. In multi-channel designs, the logical designators for repeated channel components may be the same, but each component must have a unique physical designator in the PCB design. This can be accomplished by appending the Room Name to the component name as shown in the Component Naming field below.

The Multi-Channel tab of the Project Options dialog allows you to specify the room naming style and the component designator naming format for your designs. By controlling the multi-channel designator format in this dialog, you control the mapping from the single logical component in the Schematic Editor View to the multiple physical instances on the PCB. The tab is essentially divided into two areas - Room Naming and Component Naming.

The Multi-Channel tab allows for flexible default naming formats in Multi-Channel designs.

Room Naming

Use the Room Naming Style drop-down list to define the naming format you require for the rooms in your design. These rooms are created by default when you update the project schematics to the PCB. There are five styles available — two flat and three hierarchical.

Flat room name formats	Hierarchical room name formats
Flat Numeric with Names	Numeric Name Path
Flat Alpha with Names	Alpha Name Path
	Mixed Name Path

Hierarchical room names are formed by concatenating all channelized sheet symbol designators (ChannelPrefix + ChannelIndex) in the relevant channel path hierarchy.

As you select a room naming style from the list, the graphical representation is dynamically updated to reflect the naming convention that will appear in the design. The image below gives an example of a 2x2 channel design (a nested 2 channel design, each of those channels has 2 channels within it). The larger cross-hatch regions represent the 2 upper level channels (or Banks) and the shaded regions within represent the lower level channels (with two sample components shown in each). When the design is compiled, a room is created for each sheet in the design, including each bank and each lower-level channel.
Use the Level Separator for Paths field to specify the required character/symbol for separating the path information when using the hierarchical naming styles. There are no restrictions on the character used for the Level Separator; however, a single non-alphanumeric character is easier to read.

For the 2x2 channel design shown in the image, a total of 6 rooms will be created -
one for each of the 2 Banks and one for each of the 4 lower level channels.

Component Naming

There are several designator formats available for naming components. You can choose a format or define your own using valid keywords. Define the Component Naming format by selecting from the Designator Format drop-down list. There are eight predefined formats — five flat and three that can be used in a hierarchical context:

Flat Designator Formats
$Component$ChannelAlpha
$Component_$ChannelPrefix$ChannelAlpha
$Component_$ChannelIndex
$Component_$ChannelPrefix$ChannelIndex
$ComponentPrefix_$ChannelIndex_$ComponentIndex
Hierarchical Designator Formats
$Component_$RoomName
$RoomName_$Component
$ComponentPrefix_$RoomName_$ComponentIndex

The Flat Designator Formats name each component designator in a linear progression, starting from the first channel, avoiding the duplication of designators. The Hierarchical Designator Formats include the Room Name in the designator for a component. If the Room Naming style chosen is one of the two possible flat styles, then the style for the component designator will also be flat. However, if a hierarchical style has been chosen for Room Naming, the component designator will also be hierarchical as the path information will be included in the format.

Defining your own Designator Format

You can define your own component designator format by typing directly into the Designator Format field using valid keywords. Select from any combination of the following keywords to construct the format string:

Keyword	Definition
$RoomName	Name of the associated room, as determined by the style chosen in the Room Naming Style field
$Component	Component Logical Designator (e.g. U1)
$ComponentPrefix	Component Logical Designator Prefix (e.g. U for U1)
$ComponentIndex	Component Logical Designator Index (e.g. 1 for U1)
$ChannelPrefix	Logical Sheet Symbol Designator
$ChannelIndex	Index you have specified to distinguish between different channels
$ChannelAlpha	Channel Index expressed as an alpha character. This format is only useful if your design contains less than 26 channels in total, or if you are using a hierarchical designator format

Displaying Physical Names in your Compiled Documents

Your design is constructed in the Editor tab. After you have compiled your project, Compiled Documents (physical representations of your design) are visible and can be accessed by clicking on the Compiled Document tabs, located along the bottom of the Schematic Document in the design window.

Examples of workspace tabs.

You can specify display preferences for the physical names in the Compiled Documents. Compiled Naming Expansion preferences can by customized by:

1. Selecting DXP » Preferences command which brings up the Preferences dialog. From there, go to the Schematics - Compiler tab.
2. In the Compiled Names Expansion control, choosing to expand the compiled (physical) names of Designators, Net Labels, Ports, Sheet Numbers or Document Numbers.
3. In the Compiled Names Expansion control, choosing which names you would like to be displayed in superscript. Choose to either: Never display superscript (expanded names are never displayed), Always display superscript (expanded names are always displayed) or Display superscript if necessary (expanded names are only displayed if they are different from the source)

Display preferences for physical names can be specified on the schematic - Compiler tab of the Preferences dialog. You may specify your Compiled Naming Expansion
Preferences after you perform Board Level Annotation, remembering to compile your project so that these preferences are displayed in your Compiled Document.

Compiling the project

You must compile your project in order for any changes made to room and/or component designator formats to take effect. Compile the project by selecting Project » Compile PCB Project. When your design is compiled, the Editor tab (at the bottom of the workspace) is shown in the Schematic Editor, however now, there are also Compiled Document tabs displayed along the bottom of the design window.

Once the design has been compiled, it is transferred to the Schematic Editor in the normal way (Design » Update PCB). The transfer process will automatically create a component class for each Schematic sheet in the design, a room for each component class and group the components in each class in their room, ready for placement.

PCB Annotation

Positional Annotation in PCB

A key ingredient of good board design is component layout. In a large design, a components' position on the board may have no relationship to its designator, for example, R1 may end up on the opposite side of the board to R2. To make it easy to locate a component on the board, you can re-assign the designators (re-annotate the board) positionally. To systematically assign designators in the PCB Editor based on their position, use Tools » Re-annotate which opens the Positional Re-Annotate dialog, as shown below.

The Positional Re-Annotate dialog includes a graphical representation of each method.

Each component is identified by its bounding rectangle, excluding strings. The components are sorted into a list, and the list is renumbered in that order to create the new component designations. To compare two components in the X-direction, the left-side of the bounding rectangle is used. To compare two components in the Y-direction, the edge used depends upon the renumber direction: ascending-Y, use the bottom edge; descending-Y, use the top edge.

The Comparison Threshold** option can be used as a buffer value when comparing two edges to determine if they are equal.  For example, if two left-edges are within 75.0 mils of each other, and the comparison threshold is set to 100.0mil, then these two components are considered to be at the same X-position (left-edge). This allows for slightly misaligned components to be re-numbered in a logical order, as shown in the image below. Here R27 is lower that the other resistors, to keep it correctly annotated with the adjacent resistors the Comparison Threshold** was set to 10mils. 

A series of resistors that have been positionally re-annotated, note that R27 has remained in the annotation sequence even though it is lower that the other resistors.

Annotate Scope** options also give control of the annotation process for boards with components mounted on both sides. For the Bottom-side of the board, components are re-annotated as if the designer was looking at the board flipped over. So for the X-direction comparison on the back-side, the software actually uses the right-edge of the bounding rectangle, remembering that viewed from the back-side this edge would look like the left-side.

If the Selected Components** option is enabled and re-annotation will result in a component in the selection set being given a designator that is a duplicate of an existing non-selected component, the non-selected component will have an _1 appended to its designator to ensure all designators remain unique.

Note that a rotated component is identified by the smallest bounding rectangle that encompasses the original bounding rectangle, in its new rotated orientation, as shown in the images below.

The image on the left shows the bounding rectangle for R2, the image on the right shows the new bounding rectangle when R2 is rotated.

An ASCII text file is generated (DesignName[Date][Time].WAS) in the same folder as the PCB document. The file lists initial and re-annotated designator values. Once a Re-Annotate has been performed on the PCB, you would typically pass these changes back to Schematic using the Design » Update command. The WAS file can also be used to load the changes into the schematic, if the PCB and  schematic files are in different  locations.

To prevent a component from having its designator re-assigned, enable the Protect Locked Designators** checkbox, and ensure that the Lock Strings option is also enabled in that component's properties dialog.

Controlling the Display of the Designator on the PCB

Extended Designator strings in a multi-channel design can be tedious to place in the PCB Editor. You can either choose naming options that result in a short name or display the original, logical component designation instead. For example, C30_CIN1 would display as C30. This would necessitate some other notation being added to the board to indicate the separate channels, such as a box being drawn around each channel on the component overlay.

You can select between Logical and Physical designator display on the PCB in the Board Options dialog (Design » Board Options). If you choose to display the logical designators for components in a multi-channel design, these will be displayed on the PCB and in any output generated such as prints and Gerber's. The unique physical designators, however, are always used when generating a Bill of Materials.

FPGA Annotation

An FPGA design, like a PCB design requires that each component is uniquely labeled or designated. In an FPGA design, the components are annotated using the standard annotation commands. There are annotation-related processes required in an FPGA design, detailed below.

Back-Annotation of Pin Assignments to the FPGA project

Every net in your FPGA design that leaves the device must be allocated to a device pin. For an FPGA project (*.PrjFpg), pin assignments are defined in a constraint file. Rather than manually assigning every net to a device pin, it is easier to let the vendor place and route software do this. Any pins (ports) that were not assigned in the constraint file prior to place and route are automatically assigned a physical pin during place and route. Since these assignments are needed before the FPGA design can be linked to the PCB design, and the allocation may well change during PCB layout and routing, the vendor pin assignments provide a good starting point.

To import the pin assignments from the place and route tool:

1. Open the constraint file, then select Design » Import Pin File » Select File from the menu.
2. Navigate to the appropriate vendor-generated pin file. It will be located in a folder with a name like MyFPGAProject\ProjectOutputs\ProjectBoard.
3. After selecting the pin file and clicking OK, the Constraint Editor Preferences dialog will appear. If you enable an option in the dialog, that constraint information will be extracted from the file (if it is available) and included in your constraint file.
4. Save and close the Constraint file. The design is now ready to be linked to the target PCB.

Import pin allocation directly from FPGA vendor pin files.

Back-Annotation from Vendor Pin Files to the PCB Schematic

If you are not designing the FPGA within Altium Designer, you will still need to manage the pin assignments to ensure the PCB and FPGA designs are in-sync. In the Schematic Editor for your PCB project, the FPGA component can be updated directly from the vendor pin file. Back-Annotation data support includes pin name and electrical type. This feature does not require the FPGA to have been designed in Altium Designer, all popular vendor pin files can be read directly. Right-click on the Schematic symbol for the FPGA and select Part Actions » Import FPGA Pin File from the floating context menu.

Design Synchronization - Finalizing the Annotation Process

Direct Design Synchronization is the preferred method to keep your Schematic and PCB designators matching unless you do not have access to both the Schematic and the PCB editors.
Design Synchronization compares the components and connectivity of the Schematic directly to the PCB, producing a list of differences. A list of changes required to resolve these differences is generated as an ECO (Engineering Change Order). An ECO file describes the differences between the current design and the desired design and can be executed, updating the target and bringing the design into synchronization.

Forward Synchronization and Back Synchronization

The terms Forward Synchronization and Back Synchronization are specific ways of describing the direction which annotation and design changes are transferred during the synchronization of data.
Visualizing a design flow that starts with and is driven by the Schematic, Forward Synchronization is the process of updating changes made in the Schematic Editor forward to the PCB.
Back Synchronization is the process of updating changes made in the PCB backwards to the Schematic Editor.

Forward Synchronization

There are four reasons why you would synchronize data from the Schematic to the PCB:

1. A new component is added in the Schematic Editor and is required in the PCB layout
2. You have Annotated your Schematic design for the first time or since your last design synchronization
3. In your multi-channel design, you have changed your Project Options to modify your physical (PCB) naming style
4. You have done a Board Level Annotation for the first time or since your last design synchronization.

To Synchronize your Schematic Design forward to the PCB Design:

Choose from one of the following methods to synchronize your Schematic Design forward to your PCB Design:

1. Select the Design menu in the Schematic Editor and choose the target PCB Document to update

• After launching this command, the source Schematic Documents are compiled and if any differences exist between these and the target PCB Document, the Engineering Change Order dialog appears with a list of modifications required to synchronize the PCB with the Schematic Design
• Execute changes to synchronize your design

2. Select the Design menu in the PCB Editor and choose to Import Changes from the active project, which imports changes from the Schematic Documents to the PCB document.

Back Synchronization

Back Synchronization is done when you have annotated or changed your PCB design and you want to update the Schematic design.

To Synchronize your PCB Design back to the Schematic Design:

Choose from one of the following methods to synchronize your PCB Design back to your Schematic Design:

1. Select the Design menu in the PCB Editor and choose to Update Schematics in the active project. By default, the Push Component Designator Changes to Annotation File flag in the ECO Generation tab in your Project Options is checked so changes made in the PCB Editor will be pushed to the Annotation File only and ultimately Compiled Documents upon compilation. Uncheck this flag to push changes to the source Schematic Document only (Editor view)

    
2. From the Schematic Editor, select Tools » Annotate Schematics and click the Back Annotate button in the Annotate dialog. Choose the WAS-IS file generated when re-annotating designators in the PCB environment. This is a legacy tool and the preferred method of design synchronization is the Design » Update Schematics command
3. From the Schematic Editor, select Tools » Board Level Annotate and click the Back Annotate button in the Board Level Annotate dialog. Choose the WAS-IS file generated when re-annotating designators in the PCB environment. This is a legacy tool and the preferred method of design synchronization is the Design » Update Schematics command
4. From the Schematic Editor, select the Tools » Back Annotate Schematics command. Choose the WAS-IS file generated when re-annotating designators in the PCB environment. This is a legacy tool and the preferred method of design synchronization is the Design » Update Schematics command.

Traditional Methods of Design Synchronization

Altium Designer supports the traditional intermediate (netlist and WAS/IS) file approach for Design Synchronization. Forward Synchronization of annotation data can be done through the use of a netlist file, whilst Back Synchronization can be done through the use of a WAS/IS file (listing what each designator WAS, and what it now IS). The preferred method for synchronizing your design is Direct Design Synchronization.

Component Linking with Unique IDs

If you have Re-Annotated your design, the Schematic component designators or the compiled component designators will no longer match the PCB component designators, so synchronization is required to successfully close off the design.
Rather than relying on the designator itself as the key field that relates a Schematic symbol to its equivalent PCB footprint, Altium Designer can maintain design synchronization through Unique IDentifier (UID) system. The UID is a system-generated value that uniquely identifies the source component and matches each Schematic component to the corresponding PCB component.

When a component is placed on a schematic sheet it is automatically assigned an UID. The first time component information is transferred from the source Schematic documents to a blank PCB, the UID information from each schematic component is assigned to the corresponding PCB component.
Refactoring allows you to convert Device Sheets to Schematic Sheets and vice versa while maintaining the Unique ID of the sheet and its components. In addition, you can refactor (or move) subcircuits to other schematic sheets in the current project, maintaining the Unique ID of the subcircuit. Access this command through the Edit menu or by right-clicking on either the Sheet Symbol or the sub circuit and choosing Refactor.

Altium Designer's synchronization feature, initiated by launching the Design » Update command uses these UIDs to match each Schematic component to its PCB equivalent.
Design updates/changes can then be implemented using Engineering Change Orders (ECOs). An ECO lists all modifications required to implement changes to one or more design documents, in order to satisfy the synchronization action requested.
ECOs are used to affect design updates in a variety of situations, such as:

1. SCH to PCB design updates
2. Performing Annotation updates to Schematic component designators and compiled component designators
3. Implementing updates to parameters using the Parameter Manager
4. Updating parameter information with information stored in source libraries or a company database.
   Whenever you compare the Schematic and PCB (such as when you select Design » Update) Altium Designer first matches components that share the same UID. When components are detected that do not share a UID, you are alerted and the application offers to attempt to match by designator. Until you have assigned a matching UID to both the Schematic and the PCB, you will continue to get this message.
   Unique IDs and their correlation are managed in the Edit Component Links dialog. Select Project » Component Links to open this dialog. Note that the dialog can only be opened when a PCB document is active as UID changes are always applied to the PCB rather than the Schematic. You can use the Edit Component Links dialog at any stage during the design to view the linking between the components to verify that components between documents are correctly matched, as well as to assign matching UIDs to components that are currently unmatched.