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.
Running the Autoplacer
To run the autoplacer, select
Autoroute»Start Autoplacement
.
To place only selected parts, selected
Autoroute»Autoplace Selected
Parts
.
To view the results of any autoplacement, select the
Results
tab of the
Spreadsheet View
.
Refer to the
autoplaced parameters.
Controlling the Autoplacer
The autoplacer is controlled from the
Autoplace
tab of the
Routing
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.
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
