Replace invalid characters with HTML entities
— with — ’ with ’ + with + × with x ç with ç “ with “ ” with ” ‘ with ‘ • with • – with - µ with µ † with † Fix C++ θ with θ Yen symbol instead of times Fix broken apos Bullet again E-circumflex
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James Gregory
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9e52de9586
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353 changed files with 5091 additions and 5091 deletions
18
29-02.html
18
29-02.html
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@ -48,16 +48,16 @@ MAP_MASK equ 2 ;Map Mask register index in SC
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DISPLAYED_SCREEN_SIZE equ (640/8)*350 ;# of displayed bytes per plane in a
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; hi-res graphics screen
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;
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stack segment para stack ‘STACK’
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stack segment para stack ‘STACK’
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db 512 dup (?)
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stack ends
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;
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Data segment word ‘DATA’
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Filename db ‘SNAPSHOT.SCR’,0 ;name of file we’re restoring from
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ErrMsg1 db ‘*** Couldn’‘t open SNAPSHOT.SCR ***’,0dh,0ah,‘$’
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ErrMsg2 db ‘*** Error reading from SNAPSHOT.SCR ***’,0dh,0ah,‘$’
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WaitKeyMsg db 0dh, 0ah, ‘Done. Press any key to end...’,0dh,0ah,‘$’
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Handle dw ? ;handle of file we’re restoring from
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Data segment word ‘DATA’
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Filename db ‘SNAPSHOT.SCR’,0 ;name of file we’re restoring from
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ErrMsg1 db ‘*** Couldn’‘t open SNAPSHOT.SCR ***’,0dh,0ah,‘$’
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ErrMsg2 db ‘*** Error reading from SNAPSHOT.SCR ***’,0dh,0ah,‘$’
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WaitKeyMsg db 0dh, 0ah, ‘Done. Press any key to end...’,0dh,0ah,‘$’
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Handle dw ? ;handle of file we’re restoring from
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Plane db ? ;plane being written
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Data ends
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;
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@ -80,7 +80,7 @@ Start proc near
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sub al,al ;open for reading
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int 21h
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mov [Handle],ax ;save the handle
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jnc RestoreTheScreen ;we’re ready to restore if no error
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jnc RestoreTheScreen ;we’re ready to restore if no error
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mov ah,9 ;DOS print string function
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mov dx,offset ErrMsg1
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int 21h ;notify of the error
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@ -156,7 +156,7 @@ Code ends
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</PRE>
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<!-- END CODE //-->
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<P>If you compare Listings 29.1 and 29.2, you will see that the Map Mask register setting used to load a given plane does not match the Read Map register setting used to read that plane. This is so because while only one plane can ever be read at a time, anywhere from zero to four planes can be written to at once; consequently, Read Map register settings are plane selections from 0 to 3, while Map Mask register settings are plane <I>masks</I> from 0 to 15, where a bit 0 setting of 1 enables writes to plane 0, a bit 1 setting of 1 enables writes to plane 1, and so on. Again, Chapter 28 provides a detailed explanation of the differences between the Read Map and Map Mask registers.</P>
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<P>Screen saving and restoring is pretty simple, eh? There are a few caveats, of course, but nothing serious. First, the adapter’s registers must be programmed properly in order for screen saving and restoring to work. For screen saving, you must be in read mode 0; if you’re in color compare mode, there’s no telling what bit pattern you’ll save, but it certainly won’t be the desired screen image. For screen restoring, you must be in write mode 0, with the Bit Mask register set to 0FFH and Data Rotate register set to 0 (no data rotation and the logical function set to pass the data through unchanged).</P><P><BR></P>
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<P>Screen saving and restoring is pretty simple, eh? There are a few caveats, of course, but nothing serious. First, the adapter’s registers must be programmed properly in order for screen saving and restoring to work. For screen saving, you must be in read mode 0; if you’re in color compare mode, there’s no telling what bit pattern you’ll save, but it certainly won’t be the desired screen image. For screen restoring, you must be in write mode 0, with the Bit Mask register set to 0FFH and Data Rotate register set to 0 (no data rotation and the logical function set to pass the data through unchanged).</P><P><BR></P>
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<CENTER>
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<TABLE BORDER>
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<TR>
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