The BUILD_PCS MACRO Creates a Named PHYSICAL_CONSTRAINT_SET (PCS) which can be applied to matching NetNames or referenced by an Electrical Constraint Set (ECS)
Physical Constraint Sets
A Physical Constraint Set is use to constrain the PHYSICAL attributes of signals on each routing layer.
The dal Stackup tool creates named PCS for each impedance rule extracted from the stackup spreadsheet.
If more impedance rules are needed, the BUILD_PCS macro can be used to easily define them in a few rows
BUILD_PCS can define impedance width and spacing rules for each layer as well as the minimum width required for matching power nets.
It can also create rules to exclude routing layers for target nets
BUILD_PCS
This Line tells dal constraints to create a new named PCS
syntax:
BUILD_PCS | NAME=> | NAME_FOR_PCS
the TYPE=> Attribute tells dal constraints what type of PCS the user wants to create
Valid options are: DIFF_IMPEDANCE, SINGLE_ENDED_IMPEDANCE and POWER
UNITS
The UNITS=>Attribute tells dal constraints what units to use for the PCS
Valid options are: MILS and MM
ON_LAYERS
the ON_LAYERS=> attribute lets the user exclude certain routing layers for the target nets
The ON_LAYERS attribute is converted to AllegroPCB ALLOW_ETCH contraints
All nets default to ALLOW_ETCH =1 for every layer.
The ON_LAYERS lets us turn off the ALLOW_ETCH for specific layers
Syntax:
ON_LAYERS=>-12,-15
this command says that the target nets are allowed on every layer except Layers 12 and 15
TRACE_WIDTH_PARAMETERS
the TRACE_WIDTH_PARAMETERS attribute provides a list of routing widths and spacing for each routing layer (using the UNITS attribute)
example syntax for TYPE=>DIFF_IMPEDANCE
TRACE_WIDTH_PARAMETERS=> L1,L24=10/7.5:L4,L5,L8,L9,L16,L17,L20,L21=3.7/5
This specifies that target diff_pair nets on Layers 1 and 24 should be routed at 10 mils and 7.5 mil edge to edge spacing. On layers 4,5,6,7,8,9,16,17 and 21 target diff_pairs should be routed at 3.75 mils and 5 mil spacing
example syntax for TYPE=>SINGLE_ENDED_IMPEDANCE
TRACE_WIDTH_PARAMETERS=> L1,L24=12:L4,L5,L8,L9,L16,L17,L20,L21=6
This specifies that target single_ended nets on Layers 1 and 24 should be routed at 12 mils, On layers 4,5,6,7,8,9,16,17 and 21 target single_ended nets should be routed at 6 mils
example syntax for TYPE=>POWER
TRACE_WIDTH_PARAMETERS=> L1,L24=25:L4,L5,L8,L9,L16,L17,L20,L21=18MEMBERS
The MEMBERS=> Attribute tells dal constraints what nets to apply the new PCS to.
This is an optional attribute when you are creating a PCS that will be assigned from an ECS.
The syntax is MEMBERS=>net_match1,net_match2.... net_matchN
like
MEMBERS=>P48V,P48V_RTN
This tells dal constraints to assign this PCS to any net containing 'P48V' or 'P48V_RTN'
in this case the net_match is a simple text pattern
The MEMBERS net_matches are treated as regular expressions by dal constraints and are quite powerful.
To see more information on regular expression entry see Regular Expressions In CadEnhance Tools
NOT_MATCHING
The NOT_MATCHING=>Attribute is optional and works together with the MEMBERS attribute to fully define the set of target nets
The NOT_MATCHING is a comma separated list of patterns that will be used to exclude nets from the set of nets that match the MEMBER patterns
Together the 2 attributes make very simple to define a large set of nets without having to create a very large list of specific matches
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