Q45169: PCOPY Causes Screen Snow on Some CGA Video Cards
Article: Q45169 Product(s): See article Version(s): 4.00 4.00b 4.50 Operating System(s): MS-DOS Keyword(s): ENDUSER | B_BasicCom | mspl13_basic Last Modified: 20-DEC-1989 The program below demonstrates that the PCOPY statement may produce "snow" on some CGA video cards. This is caused by a timing-dependent refresh problem common to many CGA adapters. This information applies to Microsoft QuickBASIC Versions 4.00, 4.00b, and 4.50, to Microsoft BASIC Compiler Versions 6.00 and 6.00b for MS-DOS and MS OS/2, and to Microsoft BASIC PDS Version 7.00 for MS-DOS and MS OS/2. The following program is PCOPY.BAS, which uses PCOPY to copy several lines of text to the second page of video memory. When run on a CGA system, screen "snow" will appear during PCOPY. SCREEN 0 PRINT "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa" PRINT "bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb" PRINT "Watch the snow" PCOPY 0, 1 SCREEN 0, , 1, 1
THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.
Copyright Microsoft Corporation 1986-2002.