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Chapter 7
Autorouting and Autoplacement
© National Instruments Corporation
7-3
The autoplacer places parts as clusters. These clusters are generated by
grouping a multi-pin part with a series of connected parts, each of which
has fewer than four pins. Each cluster is then assigned a placement priority.
By arranging parts into clusters, the autoplacer can place together those
parts that have multiple connections. Block capacitors, which are
connected to power signals, are always excluded from clusters. Ultiboard
uses automatic block capacitor recognition to place block capacitors close
to their corresponding ICs.
grouping a multi-pin part with a series of connected parts, each of which
has fewer than four pins. Each cluster is then assigned a placement priority.
By arranging parts into clusters, the autoplacer can place together those
parts that have multiple connections. Block capacitors, which are
connected to power signals, are always excluded from clusters. Ultiboard
uses automatic block capacitor recognition to place block capacitors close
to their corresponding ICs.
Running the Autoplacer
To run the autoplacer, select Autoroute»Start Autoplacement.
To place only selected parts, selected Autoroute»Autoplace Selected
Parts.
Parts.
To view the results of any autoplacement, select the Results tab of the
Spreadsheet View.
Spreadsheet View.
Refer to the Controlling the Autoplacer section for information about
autoplaced parameters.
autoplaced parameters.
Controlling the Autoplacer
The autoplacer is controlled from the Autoplace tab of the Routing
Options dialog box.
Options dialog box.
Complete the following steps to enter autoplacer settings:
1.
Select Autoroute»Autoroute/place Options.
2.
Click on the Autoplace tab of the Routing Options dialog box.
3.
In the Retries area:
•
Number of Retries—Enter a number from 1 to 10. This number
represents the portion of parts that will be placed in each pass. For
example, if set to “3”, the placer attempts to place one third of the
parts, then the next third, and so on.
represents the portion of parts that will be placed in each pass. For
example, if set to “3”, the placer attempts to place one third of the
parts, then the next third, and so on.
4.
In the Cost Factors area:
•
Part Pin Factor—Use to control cluster placement. When
determining which part should be placed next, the cluster placer
looks for a part that has many connections to parts that have
already been placed. This part can be either the one with the most
pins or with the greatest percentage of pins connected to parts that
have already been placed. Enter a number from 0 to 10. 0
prioritizes parts with the highest absolute number of pin
determining which part should be placed next, the cluster placer
looks for a part that has many connections to parts that have
already been placed. This part can be either the one with the most
pins or with the greatest percentage of pins connected to parts that
have already been placed. Enter a number from 0 to 10. 0
prioritizes parts with the highest absolute number of pin