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James Gregory 2013-12-31 11:38:48 +11:00
commit f658bfbb40
203 changed files with 26546 additions and 25801 deletions
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29-02.md
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@ -12,120 +12,122 @@ pages: 545-547
**LISTING 29.2 L29-2.ASM**
; Program to restore a mode 10h EGA graphics screen from
; the file SNAPSHOT.SCR.
;
VGA_SEGMENT equ 0a000h
SC_INDEX equ 3c4h ;Sequence Controller Index register
MAP_MASK equ 2 ;Map Mask register index in SC
DISPLAYED_SCREEN_SIZE equ (640/8)*350 ;# of displayed bytes per plane in a
; hi-res graphics screen
;
stack segment para stack ‘STACK'
db 512 dup (?)
stack ends
;
Data segment word ‘DATA'
Filename db ‘SNAPSHOT.SCR',0 ;name of file we're restoring from
ErrMsg1 db ‘*** Couldn'‘t open SNAPSHOT.SCR ***',0dh,0ah,‘$'
ErrMsg2 db ‘*** Error reading from SNAPSHOT.SCR ***',0dh,0ah,‘$'
WaitKeyMsg db 0dh, 0ah, ‘Done. Press any key to end...',0dh,0ah,‘$'
Handle dw ? ;handle of file we're restoring from
Plane db ? ;plane being written
Data ends
;
Code segment
assume cs:Code, ds:Data
Start proc near
mov ax,Data
mov ds,ax
;
; Go to hi-res graphics mode.
;
mov ax,10h ;AH = 0 means mode set, AL = 10h selects
; hi-res graphics mode
int 10h ;BIOS video interrupt
;
; Open SNAPSHOT.SCR.
;
mov ah,3dh ;DOS open file function
mov dx,offset Filename
sub al,al ;open for reading
int 21h
mov [Handle],ax ;save the handle
jnc RestoreTheScreen ;we're ready to restore if no error
mov ah,9 ;DOS print string function
mov dx,offset ErrMsg1
int 21h ;notify of the error
jmp short Done;and done
;
; Loop through the 4 planes, making each writable in turn and
; reading it from disk. Note that all 4 planes are writable at
; A000:0000; the Map Mask register selects which planes are readable
; at any one time. We only make one plane readable at a time.
;
RestoreTheScreen:
mov [Plane],0 ;start with plane 0
RestoreLoop:
mov dx,SC_INDEX
mov al,MAP_MASK ;set SC Index to Map Mask register
outdx,al
inc dx
mov cl,[Plane] ;get the # of the plane we want
; to restore
mov al,1
shl al,cl ;set the bit enabling writes to
; only the one desired plane
out dx,al ;set to read from desired plane
mov ah,3fh ;DOS read from file function
mov bx,[Handle]
mov cx,DISPLAYED_SCREEN_SIZE ;# of bytes to read
sub dx,dx ;start loading bytes at A000:0000
push ds
mov si,VGA_SEGMENT
mov ds,si
int 21h ;read the displayed portion of this plane
pop ds
jc ReadError
cmp ax,DISPLAYED_SCREEN_SIZE ;did all bytes get read?
jz RestoreLoopBottom
ReadError:
mov ah,9 ;DOS print string function
mov dx,offset ErrMsg2
int 21h ;notify about the error
jmp short DoClose ;and done
RestoreLoopBottom:
mov al,[Plane]
inc ax ;point to the next plane
mov [Plane],al
cmp al,3 ;have we done all planes?
jbe RestoreLoop ;no, so do the next plane
;
; Close SNAPSHOT.SCR.
;
DoClose:
mov ah,3eh ;DOS close file function
mov bx,[Handle]
int 21h
;
; Wait for a keypress.
;
mov ah,8 ;DOS input without echo function
int 21h
;
; Restore text mode.
;
mov ax,3
int 10h
;
; Done.
;
Done:
mov ah,4ch ;DOS terminate function
int 21h
Start endp
Code ends
end Start
```nasm
; Program to restore a mode 10h EGA graphics screen from
; the file SNAPSHOT.SCR.
;
VGA_SEGMENT equ 0a000h
SC_INDEX equ 3c4h ;Sequence Controller Index register
MAP_MASK equ 2 ;Map Mask register index in SC
DISPLAYED_SCREEN_SIZE equ (640/8)*350 ;# of displayed bytes per plane in a
; hi-res graphics screen
;
stack segment para stack ‘STACK'
db 512 dup (?)
stack ends
;
Data segment word ‘DATA'
Filename db ‘SNAPSHOT.SCR',0 ;name of file we're restoring from
ErrMsg1 db ‘*** Couldn'‘t open SNAPSHOT.SCR ***',0dh,0ah,‘$'
ErrMsg2 db ‘*** Error reading from SNAPSHOT.SCR ***',0dh,0ah,‘$'
WaitKeyMsg db 0dh, 0ah, ‘Done. Press any key to end...',0dh,0ah,‘$'
Handle dw ? ;handle of file we're restoring from
Plane db ? ;plane being written
Data ends
;
Code segment
assume cs:Code, ds:Data
Start proc near
mov ax,Data
mov ds,ax
;
; Go to hi-res graphics mode.
;
mov ax,10h ;AH = 0 means mode set, AL = 10h selects
; hi-res graphics mode
int 10h ;BIOS video interrupt
;
; Open SNAPSHOT.SCR.
;
mov ah,3dh ;DOS open file function
mov dx,offset Filename
sub al,al ;open for reading
int 21h
mov [Handle],ax ;save the handle
jnc RestoreTheScreen ;we're ready to restore if no error
mov ah,9 ;DOS print string function
mov dx,offset ErrMsg1
int 21h ;notify of the error
jmp short Done;and done
;
; Loop through the 4 planes, making each writable in turn and
; reading it from disk. Note that all 4 planes are writable at
; A000:0000; the Map Mask register selects which planes are readable
; at any one time. We only make one plane readable at a time.
;
RestoreTheScreen:
mov [Plane],0 ;start with plane 0
RestoreLoop:
mov dx,SC_INDEX
mov al,MAP_MASK ;set SC Index to Map Mask register
outdx,al
inc dx
mov cl,[Plane] ;get the # of the plane we want
; to restore
mov al,1
shl al,cl ;set the bit enabling writes to
; only the one desired plane
out dx,al ;set to read from desired plane
mov ah,3fh ;DOS read from file function
mov bx,[Handle]
mov cx,DISPLAYED_SCREEN_SIZE ;# of bytes to read
sub dx,dx ;start loading bytes at A000:0000
push ds
mov si,VGA_SEGMENT
mov ds,si
int 21h ;read the displayed portion of this plane
pop ds
jc ReadError
cmp ax,DISPLAYED_SCREEN_SIZE ;did all bytes get read?
jz RestoreLoopBottom
ReadError:
mov ah,9 ;DOS print string function
mov dx,offset ErrMsg2
int 21h ;notify about the error
jmp short DoClose ;and done
RestoreLoopBottom:
mov al,[Plane]
inc ax ;point to the next plane
mov [Plane],al
cmp al,3 ;have we done all planes?
jbe RestoreLoop ;no, so do the next plane
;
; Close SNAPSHOT.SCR.
;
DoClose:
mov ah,3eh ;DOS close file function
mov bx,[Handle]
int 21h
;
; Wait for a keypress.
;
mov ah,8 ;DOS input without echo function
int 21h
;
; Restore text mode.
;
mov ax,3
int 10h
;
; Done.
;
Done:
mov ah,4ch ;DOS terminate function
int 21h
Start endp
Code ends
end Start
```
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