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This commit is contained in:
James Gregory 2013-12-30 18:34:31 +11:00
commit 18011c595a
352 changed files with 6040 additions and 6040 deletions
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38
27-05.md
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@ -3,7 +3,7 @@
------------------------ --------------------------------- --------------------
Another interesting point about flipping from graphics to text and back
is that the standard mode 3 character/attribute map doesn’t actually
is that the standard mode 3 character/attribute map doesn't actually
take up every byte of the first 4000 bytes of planes 0 and 1. The
standard mode 3 character/attribute map actually only takes up every
even byte of the first 4000 in each plane; the odd bytes are left
@ -21,10 +21,10 @@ single block.
Explaining why only every other byte of planes 0 and 1 is used in text
mode and why characters and attributes appear to be contiguous bytes
when they are actually in different planes is a large part of the
explanation I’m not going to go into now. One bit of fallout from this,
explanation I'm not going to go into now. One bit of fallout from this,
however, is that if you flip to text mode and preserve the graphics
bitmap using the mechanism illustrated in Listing 27.3, you shouldn’t
write to any text page other than page 0 (that is, don’t write to any
bitmap using the mechanism illustrated in Listing 27.3, you shouldn't
write to any text page other than page 0 (that is, don't write to any
offset in display memory above 3999 in text mode) or alter the Page
Select bit in the Miscellaneous Output register (3C2H) while in text
mode. In order to allow completely unfettered access to text pages, it
@ -37,10 +37,10 @@ saved, up to a maximum of all 64K of plane 2. In the worst case, a full
128K would have to be saved in order to preserve all the memory
potentially used by text mode.
As I said, Phil Coleman’s question is an interesting one, and I’ve only
As I said, Phil Coleman's question is an interesting one, and I've only
touched on the intriguing possibilities arising from the various
configurations of display memory in VGA graphics and text modes. Right
now, though, we’ve still got the basics of the remarkably complex (but
now, though, we've still got the basics of the remarkably complex (but
rewarding!) VGA to cover.
**LISTING 27.3 L27-3.ASM**
@ -52,7 +52,7 @@ rewarding!) VGA to cover.
;
; By Michael Abrash
;
Stack segment para stack ‘STACK’
Stack segment para stack ‘STACK'
db 512 dup(0)
Stack ends
@ -63,19 +63,19 @@ rewarding!) VGA to cover.
GC_INDEX equ 3ceh ;Graphics Controller Index register
READ_MAP equ 4 ;index of Read Map register
Data segment para common ‘DATA’
Data segment para common ‘DATA'
GStrikeAnyKeyMsg0 label byte
db 0dh, 0ah, ‘Graphics mode’, 0dh, 0ah
db ‘Strike any key to continue...’, 0dh, 0ah, ‘$’
db 0dh, 0ah, ‘Graphics mode', 0dh, 0ah
db ‘Strike any key to continue...', 0dh, 0ah, ‘$'
GStrikeAnyKeyMsg1 label byte
db 0dh, 0ah, ‘Graphics mode again’, 0dh, 0ah
db ‘Strike any key to continue...’, 0dh, 0ah, ‘$’
db 0dh, 0ah, ‘Graphics mode again', 0dh, 0ah
db ‘Strike any key to continue...', 0dh, 0ah, ‘$'
TStrikeAnyKeyMsg label byte
db 0dh, 0ah, ‘Text mode’, 0dh, 0ah
db ‘Strike any key to continue...’, 0dh, 0ah, ‘$’
db 0dh, 0ah, ‘Text mode', 0dh, 0ah
db ‘Strike any key to continue...', 0dh, 0ah, ‘$'
Plane2Save db 2000h dup (?) ;save area for plane 2 data
; where font gets loaded
@ -84,7 +84,7 @@ rewarding!) VGA to cover.
; data in text mode
Data ends
Code segment para public ‘CODE’
Code segment para public ‘CODE'
assume cs:Code, ds:Data
Start proc near
mov ax,10h
@ -116,7 +116,7 @@ rewarding!) VGA to cover.
shl ah,1
loop FillBitMap
;
; Put up “strike any key” message.
; Put up "strike any key" message.
;
mov ax,Data
mov ds,ax
@ -162,13 +162,13 @@ rewarding!) VGA to cover.
mov cx,4000/2 ;length of one text screen in words
rep movsw
;
; Fill the text mode screen with dots and put up “strike any key”
; Fill the text mode screen with dots and put up "strike any key"
; message.
;
mov ax,TEXT_SEGMENT
mov es,ax
sub di,di
mov al,‘.’ ;fill character
mov al,‘.' ;fill character
mov ah,7 ;fill attribute
mov cx,4000/2 ;length of one text screen in words
rep stosw
@ -217,7 +217,7 @@ rewarding!) VGA to cover.
mov cx,2000h/2 ;restore 8K (length of default font)
rep movsw
;
; Put up “strike any key” message.
; Put up "strike any key" message.
;
mov ax,Data
mov ds,ax