PCOPY Causes Screen Snow on Some CGA Video Cards

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This article was previously published under Q45169

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SUMMARY

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

KB45169

Retired KB Content Disclaimer

This article was written about products for which Microsoft no longer offers support. Therefore, this article is offered "as is" and will no longer be updated.

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