PCOPY Causes Screen Snow on Some CGA Video Cards (45169)
This article was previously published under Q45169
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
| Modification Type: |
Minor |
Last Reviewed: |
1/8/2003 |
| Keywords: |
KB45169 |
|