Microsoft KB Archive/44237

= Hercules Page Support for SCREEN 0 and SCREEN 3 =

Article ID: 44237

Article Last Modified on 8/16/2005

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APPLIES TO


 * Microsoft QuickBasic 4.0
 * Microsoft QuickBASIC 4.0b
 * Microsoft QuickBasic 4.5 for MS-DOS
 * Microsoft BASIC Compiler 6.0
 * Microsoft BASIC Compiler 6.0b
 * Microsoft BASIC Professional Development System 7.0

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This article was previously published under Q44237



SUMMARY
The following information summarizes the use of screen pages in Microsoft QuickBasic for MS-DOS with a Hercules monochrome graphics adapter.

SCREEN mode 3 supports two screen pages, page 0 and page 1. However, SCREEN 3 has only one screen page if there is another graphics adapter installed.

SCREEN mode 0 with a Hercules adapter has only one screen page, even though other adapters support up to eight pages in text mode. This is not a problem with QuickBasic or a limitation of the adapter. QuickBasic was designed to conform to the behavior of other IBM monochrome adapters.



MORE INFORMATION
All IBM monochrome adapters assume that there is enough memory to support only one screen page in text mode, SCREEN 0. QuickBasic, being a well-behaved application, makes this assumption so that its applications can run correctly on both IBM and Hercules monochrome systems in text mode without any detectable difference to you.

The ROM BIOS function, Interrupt 10 hex with function 5 hex, &quot;Set Display Page,&quot; cannot be used to work around this problem. This BIOS function correctly changes to another display page, but QuickBasic does not utilize the BIOS and continues to write text directly to video memory to the first display page. Therefore, calling this BIOS function results only in a blank screen, which may appear to hang the machine. Setting the page back to page 0 restores the screen.

Additional query words: QuickBas BasicCom

Keywords: KB44237

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