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Q21956: Using Page 2 in SCREEN 9 Gives "Illegal Function Call" on EGA

Article: Q21956
Product(s): See article
Version(s): 2.00 2.01 3.00 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | | mspl13_basic
Last Modified: 11-JAN-1990

Question:

Why do I get an "Illegal Function Call" error message when I reference
Page 2 in SCREEN mode 9 on a computer with an EGA card? The following
is an example:

   SCREEN 9,1,2,2  'EGA mode=9, 1=colorswitch on, apage=2, vpage=2
   COLOR 2,0
   LINE (1,1)-(100,100)

Response:

Screen 9 does have two pages available, but the pages are referenced
as "0" and "1". Note that "2" is not a valid page number in screen 9.
The program will work correctly if coded as follows:

   SCREEN 9,1,1,1  'EGA mode=9, 1=colorswitch on, apage=1, vpage=1
   COLOR 2,0
   LINE (1,1)-(100,100)

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