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Written by Autodesk
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This document explains how to determine the digitizer vscan value for use with the DOS version of AutoCAD Releases 11, 12, and 13.
Overview
When using AutoCAD for DOS with a digitizer on fast computers (486-66, P60/66/90), the digitizer cross hairs will sometimes freeze for a few seconds. This happens because there is a conflict between how often AutoCAD scans its Virtual Memory Page for updating, and how frequently the digitizer scans its Page Tables for updating. To correct this problem you must use the Phar-Lap option "-vscan". This option sets the delay rate between how long AutoCAD checks the memory to see if the swap file needs to be updated. The default is 20000 milliseconds. Use the following formula to help calculate the value to use with "-vscan" option.
Determining the Value
Use the adjusted CPU speed, times 20000 (AutoCAD default value), times the number of megabytes of memory in the computer.
Adjusted CPU Speed:
386's = 1.0
486-33 = 1.25
486-66 = 1.5
P-66 = 2.0
P-90 = 2.5
P-120 = 3.0
Example: 486-66 with 16 Mb of RAM (1.5 x 20000 x 16 = 480000)
From the AutoCAD DOS directory, were the ACAD.EXE file resides,
type the following:
c:\r13\dos\>cfig386 acad -vscan 480000
NOTE: This formula is not exact, you may have to adjust the value slightly for your machine.
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