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Allegro

PCB Editor User Guide:Placing the Elements

Series XL and GXL

Product Version 16.0

June 2007


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Allegro PCB Editor User Guide: Placing the Elements

June 2007 3 Product Version 16.0

1

Overview of Placing Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Manual and Automatic Placement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Placement Tasks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2

Preparation for Placing Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Determining Design Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Automatic Placement Prerequisites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Setting Placement Grids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Creating a Non-Etch Grid for Manual and Interactive Placement . . . . . . . . . . . . . . . . 15

Creating a Grid for Interactive and Automatic Placement . . . . . . . . . . . . . . . . . . . . . . 15

Editing Placement Grids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Assigning Placement Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Identifying Components for Placement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Fixing Component Placement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Keeping Related Components in the Same Room . . . . . . . . . . . . . . . . . . . . . . . . . . . 20Keeping Related Components Close Together . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Keeping Related Components on a Net Close Together . . . . . . . . . . . . . . . . . . . . . . 20

Assigning Symbols to Groups for Real-Time DFA . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Creating a Floorplan Using Rooms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Using the ROOM and ROOM_TYPE Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Specifying Timing Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Format of the crit.dat File . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Creating a crit.dat File . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

3

Placing Elements Manually . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35Accessing Manual Placement Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Using the Placement Dialog Box . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

Contents


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Accessing Options in the Placement Pop-Up Menu . . . . . . . . . . . . . . . . . . . . . . . . . . 36

Placing Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Assigning Reference Designators to Package Symbols . . . . . . . . . . . . . . . . . . . . . . . 38

Placing Alternate Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39Placing symbols using real-time Design for Assembly DRC . . . . . . . . . . . . . . . . . . . 40

Adding Unplaced Components with Quickplace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Using Quickplace in a Design Partition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Editing Nets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Creating New Nets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Editing Pin Assignments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Renaming Nets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

Removing Nets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

Shorting Nets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46Replacing Temporary Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

Placing Components Using a Text File (PlaceText) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

The Placement File . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

4

Placing Elements Automatically. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51Automatic Placement Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

About Setting Automatic Placement Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51Before Setting Automatic Placement Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

Using INSIGHT to Set Automatic Placement Parameters . . . . . . . . . . . . . . . . . . . . . . . . 53

Running INSIGHT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

INSIGHT Warnings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

Setting Automatic Placement Parameters Interactively . . . . . . . . . . . . . . . . . . . . . . . . . . 56

Tips on Applying Weights . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

Running Automatic Placement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Prerequisites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Automatic Placement and Your Placement Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57Automatic Placement of Alternate Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

Ways of Running Automatic Placement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58


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5

Swapping Components, Functions, and Pins . . . . . . . . . . . . . . . . . 61

Interactive Swapping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61Swapping Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

Swapping Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

Swapping Pins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

Automatic Swapping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

Prerequisites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

Controlling and Running Automatic Swapping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

Setting Swap Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

How Automatic Placement Parameters Affect Swapping . . . . . . . . . . . . . . . . . . . . . . 67

Defining the Swap Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68Setting the Swap Parameters and Running Automatic Swap . . . . . . . . . . . . . . . . . . . 69

Reviewing Automatic Swapping Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

Reviewing Pin, Function, or Component Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

6

Reviewing Placement Status and Results . . . . . . . . . . . . . . . . . . . . . 73Placement Log File . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

Best Placement Results Design File . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

Placed Component Report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

Unplaced Component Report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

7

Working With Groups and Modules . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77Working with Groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

Group Members . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

Creating, Editing, and Disbanding Groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

Properties in Groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

Importing and Exporting Groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

Connecting Groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

Selecting and Finding Groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

Working with Modules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82

Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82


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Module Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

Creating Modules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

Placing Modules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

Editing Modules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89Updating Modules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

Manipulating Modules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

Generating the Module Report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90

8

Partitioning a Design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91Partitioning a Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92

Partition Databases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92Partition Membership . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93

Class/Subclass Eligibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94

Using Guideports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95

Managing Partitions with the Workflow Manager . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

Exporting Partitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

Refreshing Partitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

Importing Partitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

Communication Among Designers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

Working in a Partition Database . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98Actions Excluded After Partition Export . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

File Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

Constraint Manager . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

Testprep Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100

Allegro PCB Router Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100


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1

Overview of Placing Elements

Allegro PCB Editor provides manual and automatic tools for placing elements and swappingpins, functions (gates, inverters, or logical elements within a packaged component), andcomponents. You can also place associations of elements.

Note: Placement is not available in all Allegro PCB Editor products.

Manual and Automatic Placement

With manual placement, you can place elements individually or place elements of the sametype during one pass. You can use alternate symbols for components as you place them ona design. Alternate symbols are different representations of a particular package. You definethe alternate symbols as property values in device files for package or, if using Concept, in aConcept schematic.

In automatic placement, Allegro PCB Editor places elements based on placement propertiesyou assign that restrict or influence component positioning and part packaging.

In either manual or automatic placement, you can:

Selectively identify certain parts for placement by attaching a placement tag to them.

Optionally create a floorplan, which is a block diagram of rooms in a design. Rooms arerectangular areas that you create.

You can use rooms to keep specific logical functions or related elements together inspecific areas.

You may want to alternate manual placement with automatic placement. You can preplacesensitive or fixed parts manually, run automatic placement, and then rearrange someautoplaced parts. You could finish by optimizing the overall placement of a design withmanual placement.


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Allegro PCB Editor User Guide: Placing the ElementsOverview of Placing Elements


Placement Tasks

You can use any combination of placement and swap tools in Allegro PCB Editor. Forexample, component placement using Allegro PCB Editor typically involves the followingactivities:

Determining design requirements

Creating the items required for placement processing (such as grids or package keepinand keepout areas)

Setting basic placement controls, such as package keepout and keepin areas,placement properties, and automatic placement parameters

Running manual placement alternately with automatic placement. You can run different

iterations of automatic placement and view the placement results.

Reviewing placement status and automatic placement results

Swapping pins, gates, and parts as necessary

You can use Allegro PCB Editor swapping capabilities to decrease the average wire length oruncross ratsnest lines. Automatic swapping exchanges pins or functions (gates) according tothe controls and within the area that you define. Interactive swapping lets you swap selectedelements as well as pins or functions.

Figure 1-1 shows the placement process in Allegro PCB Editor. Figure 1-2 shows placement

in a design flow.
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Figure 1-1 Placement Process

Perform prerequisites andset placement controls.

Perform automaticplacement.

Perform manual

placement.

Swap pins, functions, andelements, as necessary.

Evaluate placement.

Yes

NoIs it a good

placement?

END

BEGIN


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Figure 1-2 Placement in a Design Flow

LIBRARY DEVELOPMENT

Create custom pad shapes

Define library padstacks

Define unique packages

Define mechanical elements

LOGIC DATA TRANSFER

Create design database

Associate schematic or create andenter third-party netlist

LAYOUT PREPARATION

Define design rules (properties andconstraints)

Define layers (cross section)

Create mechanical elements(outline, keepins, keepouts)

DESIGN LAYOUT

Placement (automatic/manual)

Routing (automatic/interactive)

DESIGN COMPLETION

Rename reference designators

Backannotate

Add power and ground planes

Run Design Rule Checking (DRC)

MANUFACTURING OUTPUT

Generate pen plots

Create artwork

Generate numerical control output

DESIGN ANALYSIS

Signal integrity analysis

EMI Compliance


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2

Preparation for Placing Elements

Before you can proceed with either manual or automatic placement, you must completecertain tasks, as well as determine design requirements. This section covers those tasks.

Determining Design RequirementsDesign considerations can influencehow you prepare for placement. Table 2-1 lists questionsto determine the design requirements for placing a design.

Table 2-1 Determining Requirements for a Design

Checklist Yes No Do this...

Does the design require that yourestrict component placement tocertain rooms?

X Create a room into which to placecertain components. Attach theROOM property to each component

to be placed in that room and attachthe ROOM_TYPE property to theroom boundary to control DRC errorreporting for rooms. Run automaticplacement for each room in thedesign.

Does the design containcomponents that must be placedin certain areas?

X Place these components manuallybefore performing automaticplacement.

Do all components in each grouphave to be in the same room orplacement area?

X Add rooms and use the ROOM andROOM_TYPE properties. SeeSetup Out lines Room Out line(roomoutline command).
http://-/?-http://%24rcoms.pdf/http://%24rcoms.pdf/http://-/?-http://%24rcoms.pdf/http://%24rcoms.pdf/


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Allegro PCB Editor User Guide: Placing the ElementsPreparation for Placing Elements


Do you want to influencecomponent positioning duringautomatic placement (for proximityto related components, rotation,mirroring, and so on) by applyingspecific weighting?

X Set the appropriate automaticplacement weight properties andparameters (see AssigningPlacement Propertiesand SettingAutomatic Placement ParametersInteractively).

Does the design use alternatesymbols?

X Define alternate symbols withproperty values. See PlacingAlternate Symbols.

Do you want to swapcomponents? X You can assign the NO_MOVEproperty to each component that isnot to be swapped (see FixingComponent Placement).

Do you want to swap functions orpins?

X Set the required controls forautomatic swapping of functions andpins (see Automatic Swapping). Youcan also swap functions and pinsinteractively (see InteractiveSwapping).

Do you want to use real-timeDesign for Assembly DRC forpackage-to-package clearancechecks during interactiveplacement?

X Use the DFA Constraints Dialogspreadsheet to define spacing rulesbetween symbol definition pairs,available by choosingSetup DFASpreadsheet(dfa_spreadsheetcommand). You can also assign theDFA_DEV_CLASS property tosymbols and create a class, to whichthe spacing values defined for theclass in the DFA Constraints Dialogspreadsheet default. See Assigning

Symbols to Groups for Real-TimeDFA.

Table 2-1 Determining Requirements for a Design

Checklist Yes No Do this...
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Automatic Placement Prerequisites

Table 2-2 summarizes the items that must exist before running automatic placement in its twomodes: interactive and automatic. Note that certain items are only recommendations.

Table 2-2 Summary of Automatic Placement Prerequisites

Placement Prerequisite Interactive Mode Automatic Mode

Package and padstacks Required Required

Netlist Required Required

Package Not required Required

See Keepin and KeepoutAreasin the Allegro PCBEditor User Guide:Preparing for Layout.

Placement grid Not required

You can define a non-etch gridfor interactive placement. SeeCreating a Non-Etch Grid forManual and InteractivePlacement.

Required

Define the automaticplacement grid as described inCreating a Grid for Interactiveand Automatic Placement.

Physical rooms Required only if floorplanningSee Creating a FloorplanUsing Rooms.

Required only if floorplanningSee Creating a FloorplanUsingRooms.

Placement tag todesignate components forplacement

Required unless placing byroom

See Identifying Componentsfor Placement

Required unless placing byroom

Design outline definedwith class BOARD

GEOMETRY andsubclass OUTLINE

Recommended

See Chapter 3, Working with

Symbols, in the Allegro PCBEditor User Guide: Definingand Developing Libraries.

Recommended

See Chapter 3, Working with

Symbols,in the Allegro PCBEditor User Guide: Definingand Developing Libraries.
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Package symbols andheight restricted areas

Recommended

See Chapter 3, Working withSymbols, in the Allegro PCBEditor User Guide: Definingand Developing Libraries.

Recommended

See Chapter 3, Working withSymbols,in the Allegro PCBEditor User Guide: Definingand Developing Libraries.

Table 2-2 Summary of Automatic Placement Prerequisites

Placement Prerequisite Interactive Mode Automatic Mode
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Setting Placement Grids

You can use grids to help control component placement. Manual placement and theinteractive mode of automatic placement use a non-etch grid, which is optional. All modes ofautomatic placement require an automatic placement grid.

Creating a Non-Etch Grid for Manual and Interactive Placement

A non-etch grid is a snap grid for placing components manually and in the interactive modeof automatic placement. It is called a non-etch grid because the grid is notused for routing.You can set an absolute control grid size and location for a non-etch grid.

The origin of the non-etch grid is the origin of a design file (0,0). Allegro PCB Editor uses theroute grid to complete pin-to-pin connections. You might want to keep the non-etch gridcompatible with the route grid to reduce the number of off-grid pins.

To create a non-etch grid and control its display, choose Setup Design Parametersandthe Displaytab of the Design Parameter Editor (prmedcommand) or the define gridcommand, described in the Allegro PCB and Package Physical Layout CommandReference.

Creating a Grid for Interactive and Automatic Placement

Allegro PCB Editor requires that you create a placement grid for the area where you run anymode of automatic placement. Automatic placement places packages only at theintersections of the placement grid lines. The grid has a class of BOARD GEOMETRY and asubclass of PLACE_GRID_TOP.

Placement grids can have the following characteristics:

Non-uniform spacing between lines

Punctures at grid line intersections to prevent placement at those locations

Different grid spacing for each placement area (rooms or the entire design)

Even if the current placement area is only a room, you must still establish a grid for the entirepackage keepin area.

Once you complete placement for an area, you can make any necessary adjustments orgenerate a new grid for the next placement area. Continue this process for each subsequentarea.
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To create a window placement grid, choose Place Autoplace Top Grids(place settopgrid command) or Place Autoplace Bottom Grids ( place set bottomgridcommand). Menu items and commands are described in the Allegro PCB and Package

Physical Layout Command Reference.

Note: If you have not created a package keepin area for the automatic placement area, firstcreate thepackage keepin as described in Chapter2, AddingGraphic Elements to a Design,of the Allegro PCB Editor User Guide: Preparing for Layout.

Editing Placement Grids

Grid-line intersections are package location for all modes of automatic placement. You cancreate a non-uniform grid to accommodate irregularly spaced components by choosing the

following for grid lines: Add Line(add line command)

Edit Move(movecommand)

Edit Copy(copycommand; see Copying Grid Lines)

Edit Delete (deletecommand

Instructions for using the menu items and commands appear in the Allegro PCB andPackage Physical Layout Command Reference.

Puncturing Intersections

You can create a point on the automatic placement grid where a component cannot be placedby removing a piece of grid line called a puncture, as shown in the Figure 2-1. By deletingintersections, you can exclude package locations for automatic placement from some designareas. Puncturing lets you eliminate a single intersection point without removing an entireline.
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Figure 2-1 Grid Line Punctures

To puncture a grid line, you use the deletecommand (menu-driven editing mode only).

Punctures


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Assigning Placement Properties

You can assign placement properties to components, functions, and nets using Edit Properties(property editcommand), described in the Allegro PCB and PackagePhysical Layout Command Reference.

Table 2-3 identifies properties that affect placement and indicates where in this chapter theyare described.

Table 2-3 Properties That Affect Placement

To... Use This Property... See...

Identify components for both modes of

automatic placement or placing specificcomponents manually

PLACE_TAG Identifying Components

for Placement

Fix component placement NO_MOVE Fixing ComponentPlacement

Keep related components in the sameroom

ROOM Keeping RelatedComponents in the SameRoom

Control DRC error reporting for rooms ROOM_TYPE Using the ROOM andROOM_TYPE Properties

Keep related components close together COMPONENT_WEIGHT

Keeping RelatedComponents CloseTogether

Keep related components on a net closetogether

WEIGHT Keeping RelatedComponents on a NetClose Together

Classify symbol definitions into user-defined classes, to which package-to-package DFA spacing values are definedon the DFA Constraints Dialog

spreadsheet, available by choosingSetup DFA Constraint Spreadsheet(dfa_spreadsheetcommand) for theclass default.

DFA_DEV_CLASS Assigning Symbols toGroups for Real-TimeDFA
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Identifying Components for Placement

Use the PLACE_TAG property to identify:

Specific components for manual placement when you choose Place Manually(place manual command). See Chapter 3, Placing Elements Manually,for details.

Components you are placing automatically

Note: When you run automatic placement, be sure to remove any previously assignedPLACE_TAG properties by using the Remove Tagoption in the Automatic Placementdialog box, accessed when you choose Place Autoplace Parameters(placeparamcommand). See Setting Automatic Placement Parameters Interactivelyfordetails.

PLACE_TAG Property and Cluster Feature

During automatic placement, the PLACE_TAG property works together with the Clusteroption in the Automatic Placement dialog box accessed when you choose Place Autoplace Parameters(place paramcommand). When Clusteris enabled, placedcomponents (those with or without the PLACE_TAG property) affect the positioning ofunplaced components:

Automatic placement considers placed components outside the placement area whenthose components have the PLACE_TAG property.

Automatic placement considers placed components insidethe placement area whenthose components do NOT have the PLACE_TAG property.

If Clusteris turned off, all components outside the placement area influence both selectionand positioning of unplaced components. Therefore, you can use the Clusterfeature toselect which components outside a placement area influence the placement in that area.

Fixing Component Placement

Use the NO_MOVE property to prevent a component from being moved after placement. You

can still change other parts of the symbol, such as text, lines, or rectangles.

If you try to move a component that has NO_MOVE assigned, Allegro PCB Editor displays amessage explaining you cannot perform the operation.
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Keeping Related Components in the Same Room

Use the ROOM property in conjunction with the ROOM_TYPE property to identify a

component to place in the same room by automatic placement. The ROOM_TYPE propertyhas several values from which you can choose to control DRC error reporting under variousplacement situations.

Both modes of automatic placement place components with an attached ROOM propertyhaving a value matching the name of the active room, even if they do not have a PLACE_TAGproperty attached.

See Creating a Floorplan Using Roomsfor other details about these properties.

Keeping Related Components Close Together

Use the COMPONENT_WEIGHT property to tell both modes of automatic placement howclosely to position heavily connected components.

You might want to initially run automatic placement with a weight greater than 50 on theconnector, using the whole design. If you add this property to more than one component ona net, the effective weight is multiplied on the net.

For more details about this property and its use, see the Allegro Platform PropertiesReference.

Keeping Related Components on a Net Close Together

Attach the WEIGHT property to a net to indicate how important it is for the components onthe net to place close together during automatic placement.

While the primary purpose of the WEIGHTproperty is to keep a net (with a highweight) short,automatic placement uses the WEIGHT property to keep the components on the net closetogether.

For more details about this property and its use, see the Allegro Platform Properties

Reference.


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Assigning Symbols to Groups for Real-Time DFA

You can classify symbol definitions into a user-defined class, to which package-to-package

Design for Assembly (DFA) spacing values (defined in the DFA Constraints Dialogspreadsheet) for the class default by using the DFA_DEV_CLASS property. The DFAConstraints Dialog spreadsheet is available by choosing Setup DFA ConstraintSpreadsheet(dfa_spreadsheetcommand).

To add or remove symbol definitions from user-defined classes, or determine the symboldefinitions with the DFA_DEV_CLASS property assigned to them, you use the DFAClassification Editor dialog box, available by clicking Show symbol classifications... onthe DFA Constraints Dialog spreadsheet. Allegro PCB Editor treats these classes ascomponents comprised of symbols to which the DFA spacing values defined for the classdefault.

For example, fifty versions of an 0805 package symbol may exist, all complying to the sameDFA rule set. A single class line entry in the spreadsheet assumes the rules for eachinstance of the 0805 class of package symbols.

Clicking Updateon the DFA Classification Editor dialog box assigns the DFA_DEV_CLASSproperty to the symbol definitions in the classes you specified. For more information onmeeting DFA requirements, refer to Using Real-Time DFA Checkingin the Allegro PCBEditor User Guide: Completing the Design.
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Creating a Floorplan Using Rooms

Floorplanning entails organizing and creating rooms in which to place specific components.Rooms are rectangular areas that you create on the top and bottom sides of the board. Whenyou choose a room as a placement area, that room becomes the active area for placementprocessing.

Using the ROOM and ROOM_TYPE properties in conjunction with each other, you can thenrestrict components to specific rooms, allowing you to functionally segregate a design andarrange components that must remain close together, as well as flag DRC errors whencertain placement situations arise.

Figure 2-2 illustrates using rooms during floorplanning. See Placing Elements Automaticallyfor details on specifying either a room or the design for automatic placement.
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Figure 2-2 Using Rooms in Automatic Placement (Interactive and Automatic Modes)

Yes

No

No

Yes

Is it a goodplacement?

Segregate the circuit into rooms

Arrange placement order of

rooms/subcircuits

Is the designplaced? Select a new room

(Automatic Mode)

Create and name rooms

Assign ROOM property tocomponents and ROOM_TYPEproperty to room boundaries(Automatic and Interactive Modes)

(Automatic Mode)

(Automatic and Interactive Modes)

Place design using active room(Automatic Mode) or

Run place area roomor quickplace(Interactive Mode)

Placementcomplete


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Using the ROOM and ROOM_TYPE Properties

Use options on the Room Outline dialog box, available by invoking Setup Outlines

Room Outline(room outline command), to create rooms and name them. BecauseAllegro PCB Editor treats room boundaries as closed polygons on the TOP_ROOM,BOTTOM_ROOM, or BOTH_ROOMS subclasses of the BOARD GEOMETRY class, ensurethat the Optionstab has these settings.

You then assign that room name to the appropriate components with the ROOM property.(Another method of creating rooms is to choose Add Rectangle(add rectcommand)and then Add Text (add textcommand) to assign a room name.)

Allegro PCB Editor uses the ROOM property name to map the components to the specifiedrooms. You can attach a room property to components during schematic creation (if using

Allegro Design Entry HDL), netlist creation, or any time during physical design.

To further refine component placement in various rooms, you can attach the ROOM_TYPEproperty to a room boundary by invoking Setup Outlines Room Outline(roomoutline command). Another method of attaching the ROOM_TYPE property to a roomboundary is to use Edit Properties(property editcommand).

By specifying HARD, SOFT, INCLUSIVE, HARD_STRADDLE, or INCLUSIVE_STRADDLEas the value of the ROOM_TYPE property, you dictate whether or not DRC errors occur, andunder what placement conditions, as the table below illustrates:

The ROOM_TYPE property may also be set on the root of the design, which then controlsbehavior for any rooms without an assigned ROOM_TYPE property. If no ROOM_TYPEproperty exists at either the room or the design level, no DRC error reporting occurs.

Component Soft Hard Hard_straddle Inclusive Inclusive_straddle

Member in room No DRC No DRC No DRC No DRC No DRC

Memberstraddlingroom

No DRC DRC No DRC DRC No DRC

Member outsideofroom

No DRC DRC DRC DRC DRC

Non member inroom

No DRC DRC DRC No DRC No DRC

Non memberstraddles room

No DRC DRC DRC No DRC No DRC
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Examples of ROOM and ROOM_TYPE Properties Effect on Placement

The following table illustrates how the ROOM and ROOM_TYPE properties interact when

various components are placed.

Component ROOM Property Value/ROOM_TYPE Property Value DRC error

UA1 SOFT/SOFT No

UB1 SOFT/SOFT No

UA41 SOFT/SOFT No

U5 None assigned/SOFT No

U6 None assigned/SOFT No

UA4 HARD/HARD No

UB4 HARD/HARD Yes

UB14 HARD/HARD Yes

U1 None assigned/HARD Yes

U2 None assigned/HARD No

UA42 HARD_STRADDLE/HARD_STRADDLE No

UB42 HARD_STRADDLE/HARD_STRADDLE NoUA22 HARD_STRADDLE/HARD_STRADDLE Yes

U7 None assigned/HARD_STRADDLE Yes

U8 None assigned/HARD_STRADDLE No

UA3 INCLUSIVE_STRADDLE/INCLUSIVE_STRADDLE No

UB3 INCLUSIVE_STRADDLE/INCLUSIVE_STRADDLE No

UA43 INCLUSIVE_STRADDLE/INCLUSIVE_STRADDLE Yes

U9 None assigned/INCLUSIVE_STRADDLE No

U10 None assigned/INCLUSIVE_STRADDLE No

UA5 INCLUSIVE/INCLUSIVE No

UB5 INCLUSIVE/INCLUSIVE Yes

UA15 INCLUSIVE/INCLUSIVE Yes

U3 None assigned/INCLUSIVE No


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For the room named SOFT, no DRC errors occur for any components placed in it, as in Figure2-3.

Figure 2-3 Component Placement with ROOM_TYPE Property of SOFT

U4 None assigned/INCLUSIVE No

Component ROOM Property Value/ROOM_TYPE Property Value DRC error


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For the room named HARD, components belonging to it may reside entirely within its roomboundary. DRC errors occur when you place a component outside this room. Anycomponents that are not members of this room, yet are placed entirely within the room

boundary, cause DRC errors, such as U1 in Figure 2-4.

Figure 2-4 Component Placement with ROOM_TYPE Property of HARD
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For the room named HARD_STRADDLE, components belonging to this room may straddlethe room boundary without generating DRC errors. DRC errors occur when components areplaced completely inside the room boundary, such as UA 22 in Figure 2-5.

Figure 2-5 Component Placement with ROOM_TYPE Property of HARD_STRADDLE


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For the room named INCLUSIVE_STRADDLE, all components may reside entirely in theroom or to straddle the boundary without generating DRC errors. DRC errors occur whencomponents belonging to this room are placed entirely outside it, such as UA43 in Figure 2-6.

Figure 2-6 Component Placement with ROOM_TYPE Property of INCLUSIVE_STRADDLE


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For the room named INCLUSIVE, DRC errors occur when components belonging to itstraddle the room boundary, such as UB5 and UA15 in Figure 2-7.

Figure 2-7 Component Placement with ROOM_TYPE Property of INCLUSIVE


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Specifying Timing Data

If you want automatic placement to be aware of timing data, you must supply that data in acrit.dat file, which must be located in the same directory as the design.

Note: Whenyouuse a crit.dat file, choose Place Autoplace Design(place areadesigncommand) to specify the area for automatic placement. The menu item andcommand are described in the Allegro PCB and Package Physical Layout CommandReference.

The crit.dat file must contain the following information about each critical path:

Critical path name

Total allowable length

One or both of the following:

Included pin-pair definitions

Alternate pins for the beginning or end of the path

Format of the crit.dat File

Use a text editor to create the ASCII file that you name crit.dat. The format of thecrit.dat file is explicit:

Each critical path definition begins with the keyword PATH, on a line with fields thatspecify the name of the path and the path length definition.

Each alternate net definition or pin-pair definition for the critical path appears on aseparate line.

Alternate net definitions begin with the keyword ALT.

Use ALTwhere the total path length is critical and Allegro PCB Editor can choosethe critical connection from the nets you provide as alternatives.

ALTcan exist only as the first or last definition in the critical path.

The ALTdesignation gives automatic placement the flexibility to try differentplacement possibilities, because only the longest of the alternatives needs to beconsidered in the distance calculation.

A single ALT line may occur in a file when the definition does not require a specificpin-to-pin designation.
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The pin-pair definitions begin with the keywordPP, and alert Allegro PCB Editor thatthe corresponding pin-pair must be calculated in the order presented.

The following is an example crit.dat file:

Example crit.dat File

Creating a crit.dat File

1. In the directory that contains the design, use a text editor to open a file calledcrit.dat .

2. Begin each critical path definition using the following format:

PATH

PATH Keyword that begins a critical path definition. All fieldsfollowing it, until the next occurrence of PATH, define thecritical path.

Identifies the critical path. Type a character string with a

maximum length of 63 characters.

Specifies either a maximum length or a maximum time. In alength string, processing assumes the numbers are in userunits. To specify a time string, provide the number andappend either n (to indicate the value is in nanoseconds) orp (for picoseconds).

PATH SEL0-RAS0 .45n

ALT NET U33.1

ALT NET U33.2

ALT NET U33.3

PP U33.7 U13.12

PP U13.11 RP6.5

ALT RP6.12 NET

PATH SEL1-RAS1 5000ALT NET U33.1

ALT NET U33.2

ALT NET U33.3

PP U33.9 U13.9

PP U13.8 RP6.6

ALT RP6.11 NET

Critical path SEL0-RAS0

Critical path SEL1-RAS1


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3. Specify the first definition in the critical path.

If the total path length is critical, use the ALTformat to specify the first definition in the

critical path.ALT NET .

You must use the same format for all subsequentALT lines for the same connection. AllALTlines for a single net must be consecutive and for the same component.

For example

ALT NET U33.1

ALT NET U33.2

ALT NET U33.3

If your critical path must follow an exact order defined by pin-pairs, type the pin-pairs inthe following format:

PP . .

4. Specify additional path definitions, as required.

If ALTis the last definition in the critical path, the format must be:

ALT . NET

5. Save the file.

Specifies the reference designator.

Specifies the pin number.


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3

Placing Elements Manually

Before you can proceed with manual placement, you must complete certain tasks, as well asdetermine design requirements. See Chapter 2, Preparation for Placing Elements,fordetails.

Using manual placement, you can place all components individually, or you can placecomponents of the same type during one pass. For example, you can place all input/outputcomponents one at a time, then all ICs one at a time, then all discretes. Using the Quickplacefeature lets you put all unplaced components outside the board outline of a design.

If your system includes automatic placement, you can alternate manual with automaticplacement to:

Preplace sensitive or fixed components

Rearrange particular components placed automatically

Optimize the overall placement of a design

For information on swapping components, pins, or functions during manual placement, seeInteractive Swapping.

You can generate a report on the placed or unplaced status of the design at any time. SeeReviewing Placement Status and Resultsfor details.

Accessing Manual Placement Features

Manual placementoffersoptions for placing specificgroups of unplaced elements in a design.You can place any of the following:

ICs

I/Os

Discretes

Symbols (package, mechanical, format)


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Allegro PCB Editor User Guide: Placing the ElementsPlacing Elements Manually


Module instances

Module definitions

Allegro PCB Editor places only the elements that you specify in the Placementdialog box,shown in Figure 3-1. Each element in the specified group displays individually, with its symbolorigin on the cursor.

Using the Placement Dialog Box

You place design elements by choosing Place Manually(place manualcommand),which invokes the Placementdialog box, described in the Allegro PCB and PackagePhysical Layout Command Reference. The tabbed user interface allows you to choose forplacement (either from the database or from the library files to which you have access)symbol types, components by reference designator, and modules.

Figure 3-1 he Placement Dialog Box Tabs

Accessing Options in the Placement Pop-Up Menu

Various placement operations also feature a pop-up menu that lets you access options forcontrolling the operation.
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To use the pop-up menu during a placement operation:

1. Choose the appropriate placement option.

2. Click right to display the pop-up menu.

3. Click right to make a selection from the menu.

The following selections are standard to many pop-up menus:

Doneimplements any changes made during the operation and quits the current mode(for example, swap function mode or move mode).

Oopscancels the last operation you performed in the current mode and keeps you inthat mode.

Cancelcancels the current operation and quits the mode.

Nextimplements the last operation and keeps you in the current mode.

Movechanges the position of the selected element and keeps you in that mode.

Mirrorrelocates the currently selected symbol you want to add to the drawing to theopposite side of the board.

Rotaterotates the currently selected symbol.

These selections are unique to Place Manually(place manualcommand).

Alt Modulechooses a different module definition for the current module instance.

Alt Symbolchooses a different symbol for the current symbol selection.

Showappears on the pop-up menu if you selected Autohideon the Placement dialogbox. Selecting Showfrom the pop-up menu causes the Placement dialog box to re-appear once all elements have been placed. If Autohide is not selected, you must useShowto display the Placement dialog box.

Placing Symbols

You can place a package, mechanical, or format symbol in a design. Then you assign areference designator to a package symbol, described below. This method of placement canbe useful when you place components before the netlist is completed.


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Assigning Reference Designators to Package Symbols

Choose Logic Assign RefDes(assign refdes command), described in the Allegro

PCB and Package Physical Layout Command Reference, to assign a referencedesignator to a placed package symbol.

You can specify the increment to use when assigning a group of reference designators tosymbols. For example, use an increment of 1 to assign reference designators U1, U2, U3,and so on. Use an increment of 10 to assign reference designators U10, U20, U30, and so on.

Reference designators must already be in the database as defined in the netlist. To do this,chooseFile Import Logic(netincommand), described in the Allegro PCB andPackage Physical Layout Command Reference. You add electrical data for the symbolusing the netlist as well.
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Placing Alternate Symbols

When you place a symbol, you can use one of the following:

The symbol, which is initially attached to the cursor

The alternate symbol, by choosing the Alt Symboloption in the pop-up menu to attachan alternate symbol to the cursor

Youcan use alternate symbols for components as you place them in a design if you previouslyattached the ALT_SYMBOLS property type to the components using the Cadenceschematic-capture tools Concept HDL or Capture. ALT_SYMBOLS defines an alternatepackage symbol that can be substituted for the primary package symbol. Or, if you are usinga third-party schematic, in thedevice file, assign the ALT_SYMBOLS property to componentsby specifying a PACKAGEPROP property record. To do that, see Specifying DefinitionProperties in a Device Filein the Allegro PCB Editor User Guide: Defining andDeveloping Libraries.

When you place an alternate symbol, Allegro PCB Editor shows a list of alternate symbolsthat are valid for the processed subclass (for example, TOP symbols if TOP is being placed).The valid side is the TOP, unless you chose Mirroron the Optionstab of the control panelor in the Drawing Options dialog box, in which case, it is the BOTTOM.

You can limit the primary package symbol to the TOP or BOTTOM by using theALT_SYMBOLS_HARD property. For more information on this property, seeALT_SYMBOLS_HARD in the Allegro Platform Properties Reference.

Note: When building symbols, do not create them for the BOTTOM side of the design.Instead, build all symbols for the TOP and then mirror the symbols when placing to theBOTTOM.

Mirroring and Alternate Symbols

The Mirroroption mirrors whatever symbol is appropriate for that layer. If the symbolchanges, Allegro PCB Editor displays the name of the new symbol in the message line. Whenyou use alternate symbols, the Mirroroption uses only the symbol and the alternate symbol

you choose from the pop-up menu. If no alternate symbol exists, the symbol attached to thecursor mirrors. If the current symbol is valid for the other side of the design, it is used;otherwise, the first alternate symbol found in the property value for the side being mirroredappears with the cursor.
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Placing symbols using real-time Design for Assembly DRC

During interactive placement, real-time Design For Assembly (DFA) design rules hone the

precision and accuracy of package-to-package clearances. You create an external rules-driven table to define spacing rules between symbol definition pairs with the DFA ConstraintsDialog spreadsheet, available by choosingSetup Constraints DFA ConstraintSpreadsheet(dfa_spreadsheetcommand). These spacing values can then be appliedto a Allegro PCB Editor design while the external file remains intact on disk. You can alsoassign the DFA_DEV_CLASS property to symbols and create a class in the DFAClassification Editor (available by clicking Show symbol classifications... on the DFAConstraints Dialog spreadsheet) to which the spacing values defined for the class default.

After you define DFA rules between specific components, as you place components, spacingcircles appear on screen that highlight potential DFA rule violations when components are

placed closer than specified DFA spacing constraints, or if no constraints are supplied, whenDFA place-bounds touch or intersect. These spacing circles indicate the spacing value youset for the components when placement achieves tangency; that is, placed componentsadhere to DFA spacing rules without touching or intersecting. The placement grid you defineddetermines the degree of tangency. A 1-mil grid allowest the greatest potential for tangency,for instance. To eliminate any cursor hesitation during placement of DFA-governedcomponents, you can choose Setup User Preferences(envedcommand) to set thedfa_pauseenvironment variable to zero.

If the spacing value is 50 mil, you can instantiate the component at the spacing circle locationwhere tangency is achieved, or at a location that triggers a DRC if you wish to ignore the DRC

feedback. For more information on meeting DFA requirements, refer to Using Real-Time DFACheckingin the Allegro PCB Editor User Guide: Completing the Design.
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Adding Unplaced Components with Quickplace

The Quickplace feature lets you easily add unplaced components to the board design. Youplace logic bearing symbols outside the board outline, in either a default or user-definedconfiguration, creating a palette of symbols that you can view, filter, and move into the design.You also can place components by property/value, room, schematic page number (only withAllegro Design Entry HDL as the front end), or selection.

Choose Place Quickplace(quickplace command) to filter the types of components youwant to place on the outside edges of the board outline.

Allegro PCB Editor places components in a non-rotated state along the edge of the boardgeometry boundary. If Quickplace does not detect a board outline, an error messageappears. If the boundary is not rectangular, Quickplace creates a minimum outside rectangle(not a design element) whose minimum and maximum extents are the outer edges of theboundary geometry, as shown in Figure 3-2.

Figure 3-2 Board Geometry Rectangle

Independent of which edge or layer on which you elect to place them, Quickplace places thecomponents adjacent to one another based upon their extents.
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Once you place the components, a message at the bottom of the dialog box displays status.You can access the log file directly from the dialog box to get details of the placementoperation, as shown in Figure 3-3.

Figure 3-3 Example of quickplace.log File

Using Quickplace in a Design Partition

Quickplace can also place components within a design partition.

In the Quickplace dialog box, choose which components to place in the Placement Filtersection. Next, choose Place by Partitionand select the partition name.
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Quickplace begins component placement on the top of the board until full, and then resumesplacement on the bottom of the board. Quickplace toggles between the top and bottom of theboard, continuing to place components in an overlapped, offset pattern, until all components

are placed, as shown in Figure 3-4.

Figure 3-4 Place by Partition

1. In the Placement

Filterarea, specifywhich components to

place.

2. Choose Place by

Partitionand select

the partition namefrom the pulldownlist.

4. The componentsappear within thepartition.

3. Click Placeto add

the components.
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If the partition boundaries extend beyond the design boundaries, Quickplace continues toplace the components along the partition edges, as shown in Figure 3-5.

Figure 3-5 Partition Boundaries that Extend Beyond Design Borders
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Editing Nets

During the placement phase of a design, you may need to edit the logical connections of setsof vias and pins (otherwise known as nets). This section covers the net editing methodology.Choose Logic Net Logic(net logiccommand), described in the Allegro PCB andPackage Physical Layout Command Reference.

Net editing functionality includes:

Creating new nets

Editing pin assignments

Renaming nets

Removing nets

Shorting nets

Creating New Nets

You can create new nets in various ways. Prior to release 14.0, nets had to be imported froma netlist file, using File Import Logic (netincommand) or thenetrevcommand,described in the Allegro PCB and Package Physical Layout Command Reference.Those commands are still available and are the preferred method if you change the design

extensively. Where few changes are necessary, however, net editing within Allegro PCBEditors user interface can be more efficient. Nets that you create are immediately availablefor pin assignment, and status messages in the console window prompt display success/failure feedback.

For instructions, see Creating a Netin the Allegro PCB and Package Physical LayoutCommand Reference.

Editing Pin Assignments

Using Logic Net Logic(net logic command) settings of the Optionstab, you cancreate and change pin assignments on selected nets. Unassigned pins are immediatelyattached to a selected net; if a pin is currently attached to a net, the new net replaces theexisting one. All the objects connected to the pin are similarly updated to the new net.Unassigning a selected pin replaces the current net with a dummy net, along with all theobjects attached to the pin. The Ripup Etchoption deletes the etch connected to adeassigned pin back to the next pin or junction with no effect on other objects on the net.
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For instructions on assigning and unassigning pins, see Editing Pin Assignmentsin theAllegro PCB and Package Physical Layout Command Reference.

After creating or editing a net, use the net schedulecommand to fix its scheduling.

Renaming Nets

This feature incorporates one-step renaming of nets. When you choose an existing net torename in the Options tab, all of the nets pin assignments, property information, and otherdata is retained. In addition, properties on other objects that refer to the renamed net(XTALK_IGNORE_NETS) are updated. The renamed net is immediately available for furtherediting.

For instructions, see Renaming a Net in the Allegro PCB and Package Physical LayoutCommand Reference.

Removing Nets

You can choose any listed net in the Options tab for removal. A confirmation window appearsbefore the command completes. You do not have to reassign pins to a dummy net if thetargeted net includes assignments; the command reassigns the pins automatically.Properties on other objects that referred to the deleted net (NET_SHORT andXTALK_IGNORE_NETS) are updated.

For instructions, see Removing a Net in the Allegro PCB and Package Physical LayoutCommand Reference.

Shorting Nets

Nets that you have brought in to a design from a schematic capture may have been connectedtogether with pseudo pins assigned with the NET_SHORT property. The NET_SHORTassignment eliminates DRCs that would otherwise occur from creation of the pseudo pins.

In Allegro PCB Editor, you can short unconnected nets together without generating DRCs ina similar fashion by adding the NET_SHORT property to pins and vias that bridge planes. Thesyntax of the NET_SHORT property is:

::...

For example:

NET_SHORT = GND1:GND2
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Use Edit Propertiesor the property edit command to choose vias to which to attachthe NET_SHORT property. This procedure is described in Assigning a Property to a DesignElement.

Replacing Temporary Symbols

Allegro PCB Editor lets you replace temporary symbols you may have created on the fly inSPECCTRAQUEST with information from your product library. To do this, choose Place Replace SQ Temporary Devices(replace temp_symbolscommand), describedin the Allegro PCB and Package Physical Layout Command Reference.

Placing Components Using a Text File (PlaceText)Allegro PCB Editor lets you place components on a design using the ASCII text fileplace_txt.txt, which specifies component positions and orientations. This placement fileis created primarily for use as input for a future design. These are the commands you can use:

The plctxt outcommand generates the place_txt.txtfile from an existingdesign.

The plctxt in command places components in a new or an existing design using theplace_txt.txtfile.

The plctxtcommand places or exports components in batch mode using theplace_txt.txtfile.

All these commands are described in the Allegro PCB and Package Physical LayoutCommand Reference.

Whenyou use a placement file as input for a design, the place_txt.txt file must be inyourcurrent directory.

Make sure that the devpath and psmpath variables in your environment file point to thecomponents you are loading. Type set at the Allegro PCB Editor command prompt to displaythe Defined Variables window and view the devpath and psmpath strings. To set or edit these

variables, choose Setup User Preferences(enved command), described in the AllegroPCB and Package Physical Layout Command Reference. The devpathenvironmentvariable is in the Config_paths category, and psmpath is in the Design_pathscategory.
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The Placement File

This section contains reference information on the default placement file, place_txt.txt.

This information may be useful if you decide to edit any of the data in the file.

A placement file contains up to six columns of numbers. Each line describes the placementof a single component, as follows:

REFDES x y

The reference designator and X,Y coordinates are the only elements that always appear forevery component.

Figure 3-6shows part of a sample place_txt.txtfile. Notice that all four componentsuse a DIP16 package (no alternate symbols). The first two are not rotated; the last two arerotated 90 degrees. The space between the rotation column and thesymbol column indicatesno components are mirrored.

Figure 3-6 Sample place_txt.txt File

UUNITS = MILS

R2 2275.000 4275.000 270 RC0805

R1 2350.000 5150.000 0 m RC0805

U2 2350.000 4575.000 90 DIP14_3

REFDES Reference designator

x X-location coordinate

y Y-location coordinate

r Rotation angle

The angle can be a whole number or a fraction. Default is 0 degrees.

m Mirrored

Default is no mirroring: place on TOP.

s Symbol name

This specification is used to indicate an alternate symbol. The defaultis to use the default symbol from the device file.
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U1 2025.000 4975.000 0 m DIP14_3

You can use any text editor to edit the placement file. Observe the following conventions:

Use white-space and comments, as required.

Enclose comments in parentheses ( ).

Use either upper- or lowercase letters. Allegro PCB Editor always stores referencedesignators and symbol names in uppercase.

Decimal points are acceptable when specifying locations and angles.

Allegro PCB Editor outputs the units of a design when it creates a placement file. When youuse the file as input to a new design, Allegro PCB Editor looks for the design units andpresents the output in the units appropriate to the new design.


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4

Placing Elements Automatically

Before you can proceed with automatic placement, you must complete certain tasks, as wellas determine design requirements. See Chapter 2, Preparation for Placing Elements,fordetails.

Allegro PCB Editor can place elements automatically based on controls that you specifybefore activating automatic placement. You choose the elements to be placed and define anarea in which to place them. You can specify additional placement controls by definingplacement parameters, and properties assigned to functions and elements.

You should manually place a seed component to control automatic placement within an area.

Automatic Placement Modes

Allegro PCB Editor provides two modes for running automatic placement:

Automatic mode

In this mode, Allegro PCB Editor quickly places all tagged elements on the design. Youcan then examine the placement and reposition any elements that are not optimallyplaced, usingautomatic placement, manual placement (described inChapter 3, PlacingElements Manually), or automatic or interactive swapping (described in Chapter 5,Swapping Components, Functions, and Pins).

Interactive mode

In this mode, Allegro PCB Editor places the tagged elements on the design one at a time.It optimally locates each component and then allows you to accept or edit the location.

About Setting Automatic Placement Parameters

Before running automatic placement, you must set specific parameters that dictate:

Which placement algorithm to use


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Allegro PCB Editor User Guide: Placing the ElementsPlacing Elements Automatically


Which point on the component to use as the origin

What weights to apply to determine component positioning

How to handle elements that it cannot place

Whether to allow elements to overlap

Whether to allow placement outside the placement area

Whether to cluster heavily connected components

How to display ratsnesting

Whether to remove place tags upon completion

How to specify timing data during placement

How many iterations to perform, to a maximum of 10

Allegro PCB Editor offers two ways to set the automatic placement parameters. You can dothe following:

Use INSIGHT to set the parameters automatically, described below.

Set the parameters interactively using the Automatic Placement dialog box, described inSetting Automatic Placement Parameters Interactively.

Note: When you set the parameters interactively, you can also run automatic placement

in automatic mode.

Before Setting Automatic Placement Parameters

Regardless of which method you use to set parameters, you need to do the following beforesetting them:

Create a placement grid as described in Creating a Grid for Interactive and AutomaticPlacement.

Define package keepins and, if necessary, rooms into which you are placing design

elements. See Automatic Placement Prerequisitesfor information about the types ofareas you can create and how to create them.

Assign the PLACE_TAG property and any other properties to the components you areplacing.


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Using INSIGHT to Set Automatic Placement Parameters

The INSIGHT program determines the best automatic placement parameters for a design,based on certain restrictions that you specify. INSIGHT prepares Allegro PCB Editor to runthe automatic placement command by doing the following:

Setting weights for rotation, direction, and mirroring based on the values you provide inthe INSIGHT form.

INSIGHT sets rotation weights to produce the vertical or horizontal orientation youspecify. It sets north, south, east, and west weights to produce a placement flowconsistent with the aspect ratio of the active placement area. It sets the mirror weight toproduce a single- or double-sided placement as you specified.

Checking the design for consistency and readiness for placement. Issuing warnings of potential problems.

Properties and INSIGHT

There is only one property that INSIGHT sets. INSIGHT looks at the nets you have specifiedas power and ground and assigns them a WEIGHT property of zero. This reduces the cost ofcalculation during autoplacement, especially if the nets specified as power and ground areembedded planes.

Because INSIGHT does not process properties, except as described in the precedingparagraph, you must define any of the following optional property controls before runningautomatic placement:

Add or remove GROUP property

Set the COMPONENT_WEIGHT property

Add or remove the PLACE_TAG property

Change or add the WEIGHT property to nets other than those designated as power andground

Add or remove ROOM properties

See Assigning Placement Propertiesfor information on setting these properties.

Running INSIGHT

Note: Be sure to follow the tasks listed in Before Setting Automatic Placement Parameters.


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To use INSIGHT, choose Place Autoplace Insight(place insightcommand),described in the Allegro PCB and Package Physical Layout Command Reference.

If you need to change any parameters after INSIGHT has run, edit the Automatic Parametersdialog box, described in Setting Automatic Placement Parameters Interactively.

INSIGHT Warnings

In addition to assisting in parameter setting, INSIGHT also verifies that a design is ready forplacement.

INSIGHT issues the messages described in this section during verification. The followingconventions are used in the text of the error messages:

E indicates an error message.

W indicates a warning message.

Design Level Messages

E-Missing placement keepin rectangle

You have not defined a package keepin for use by automatic placement.

W-Unplaced components are not PLACE TAGGED.

Automatic placement requires one of the following:

PLACE_TAG properties on the components to place

An active room (that is, the placement area is a room) and components with thecorresponding ROOM property

For information on placement properties in automatic placement and on placing by room, seeAssigning Placement Propertiesand Creating a Floorplan Using Rooms.

W-No preplaced component is in area you are placing

You have not placed a seed component interactively. If you do not place a seed component,automatic placement places one for you. For optimal results, place the seed component forthe active area manually.


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Grid Level Messages

E-A placement grid was not found

Choose Place Autoplace Top Grids(place set topgridcommand) or Place Autoplace Bottom Grids(place set bottomgridcommand) to define the grid forautomatic placement. The Allegro PCB and Package Physical Layout CommandReferencedescribes both commands.

E-Grid subclass doesnt match the requested side.

You have not defined the automatic placement grid for the side you have chosen forplacement. Choose Place Autoplace Top Grids ( place set topgrid command) orPlace Autoplace Bottom Grids (place set bottomgridcommand) to define topor bottom or both grids for automatic placement. Both menu items and commands aredescribed in the Allegro PCB and Package Physical Layout Command Reference.

Messages When Room is the Active Area

E-Room was not found

Be sure that you have added the room to the design and that you specified the correct room

name in the Areadefinition.

E-Subclass of room doesnt match the placement grid

You have not defined the automatic placement grid for the side of the design where the activeroom is located. Choose Place Autoplace Top Grids (place set topgridcommand) or Place Autoplace Bottom Gr ids ( place set bottomgrid command)to define top or bottom or both grids for automatic placement. The Allegro PCB andPackage Physical Layout Command Referencedescribes both commands.

E-Subclass of room doesnt match the requested side

The subclass of the active room identifies a different side of the design from the side youspecified for placement.
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W-No unplaced component matches active room

You have requested automatic placement for an active room whose components (with

matching ROOM property) are all already placed in the design. Automatic placement placesin the room any unplaced components with a PLACE_TAG property.

Setting Automatic Placement Parameters Interactively

Note: Be sure to follow the tasks listed in Before Setting Automatic Placement Parameters.

You set automatic placement parameters interactively by using the Automatic Placementdialog box. This dialog box also allows you to run automatic placement in automatic mode.

If you have not run INSIGHT to set the parameters in this dialog box (described in UsingINSIGHT to Set Automatic Placement Parameters), the initial settings reflect system defaults.Each parameter in the dialog box guides placement within the active placement area: a room,a window, or the entire design.

If you choose to also run automatic placement from this dialog box, be aware that automaticplacement run in automatic mode finishes quickly. One way to become more familiar with theplacement parameters is to run automatic placement using the default settings on theAutomatic Placementdialogbox. After you study the results, adjust one placementparameterat a time interactively, and rerun automatic placement for the same placement area.

As the automatic placement process occurs within a placement area, the weightedparameters help automatic placement make decisions based on connection to the seedcomponent.

To set automatic placement parameters and/or run automatic placement in automatic mode,choose Place Autoplace Parameters(place paramcommand), described in theAllegro PCB and Package Physical Layout Command Reference.

Tips on Applying Weights

When you apply weights in the Automatic Placement dialog box:

Try different weight values and rerun the placement program to observe the results.

Cadence recommends that you run placement on one area of the design so, if resultsare unsatisfactory, you can change the parameters and rerun automatic placement.

To determine which parameters give you the best placement results, adjust oneparameter at a time.


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For example, if rotation is important to you, concentrate on accomplishing the desiredrotation and use the default values for direction, mirror, and straightness.

Values you set for direction, mirror, and straightness affect automatic swapping.The WEIGHT and COMPONENT_WEIGHT properties also affect swapping.

Running Automatic Placement

Prerequisites

Before running automatic placement in either mode, be sure to do the following:

Perform all the necessary prerequisites, including defining a package keepin and anautomatic placement grid as described in Automatic Placement Prerequisites.

Set the automatic placement controls as described in Using INSIGHT to Set AutomaticPlacement Parameters.

Documents

Al Gro Place