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Written by Autodesk
Return to SEA Digitizer Support Page
Summary: This document explains how to solve digitizer performance problems such as slow or jerky crosshair motion.
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Product(s) |
Release(s) |
Platform(s) |
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AutoCAD |
R10,11,12,13 |
DOS/386 |
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Audience: |
For Public Distribution - Global | |
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Keywords: |
DIGITIZER PERFORMANCE JUMPY CROSSHAIR 1205 | |
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Related documents: |
None | |
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Document: CH-ME-TD141205.DOC |
Revision: 3.2 | |
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Creation date: April 18, 1996 |
Last revised: March 24, 1998 |
Expires: March 24, 2003 |
The tips, tricks, examples and suggestions outlined in Autodesk Product Support technical documents are suggested for use at your own risk. Document contents are subject to change without notice. Autodesk is not responsible or liable for damage or events that may occur as a result of following suggestions from any Autodesk Product Support technical document.
© 1996 Autodesk. Autodesk and the Autodesk logo are registered trademarks of Autodesk Inc. All other brand names, product names or trademarks belong to their respective holders.
Table of Contents
Introduction
AutoCAD releases using the Phar Lap DOS Extender can sometimes exhibit problems when moving the crosshair on the screen. This problem is only experienced when using a digitizer. The problem will manifest itself by the digitizer seeming unresponsive resulting in slow or jerky motion of the crosshair.
The following recommendations can solve problem.
Phar Lap switch settings
The Phar Lap switch settings for -vscan and -vslen can cause symptoms as described in the summary (for polled mode digitizers).
This is caused by Phar Lap taking over to do a scan of its memory page tables. In polled mode AutoCAD is polling the digitizer at timed intervals to see if anything has changed. Occasionally AutoCAD's poll timing and Phar Lap's scan timing overlap and the digitizer polling is skipped. In interrupt mode, the digitizer tells AutoCAD when it has changed instead of waiting for AutoCAD to ask. This means there is no poll to be skipped.
To improve the situation:
1. Increase the setting on the Phar Lap's -vscan switch.
(This switch holds the value, in milliseconds, between page table scans)
2. Decrease the setting on the Phar Lap's -vslen switch.
(This switch tells Phar Lap's Virtual Memory Manager how much memory to allow for in its page tables. The default is 4 GB, but you should set it to the total amount of [disk space + RAM, expressed in bytes] that AutoCAD/Phar Lap has access to i.e. the total amount of virtual memory Phar Lap's VMM will have access to.)
Configuration (cables, switch settings, serial port conflicts)
Follow the cabling and switch settings documented in the Installation Guide for your release of AutoCAD. Some Video Display cards can conflict with the serial ports COM3 or COM4. To avoid this, connect the digitizer to either COM1 or COM2.
Digitizer driver configuration definitions
Some digitizer drivers can be configured to operate in different modes. If possible try altering the settings between Polled and Stream mode.
Polled mode
AutoCAD is polling the digitizer to get its current position and button status. The digitizer sends nothing until it receives this "polling sequence".
Stream mode
The digitizer is continually sending streams of data regarding its current position and button status to AutoCAD.
Interrupt mode
You can use interrupts to run the serial port to receive and assemble information from the digitizer. It is independent of stream- and polled-mode. AutoCAD gets interrupted with the digitizer data when a certain amount of information has been changed.
New or updated digitizer drivers
If the suggestions in this document do not resolve the problem, contact your digitizer device vendor to find out if there is a new or updated driver available for your device.
Return to SEA Digitizer Support Page
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