Misc/abrash-black-book
Watch
1
0
Fork
You've already forked abrash-black-book
 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

Normal quotes

Browse source
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
Download patch file Download diff file Expand all files Collapse all files

52
29-04.md
View file

@ -2,13 +2,13 @@
[Previous](29-03.html) [Table of Contents](index.html) [Next](29-05.html)
------------------------ --------------------------------- --------------------
How does one go about setting the palette registers? Well, it’s
How does one go about setting the palette registers? Well, it's
certainly possible to set the palette registers directly by addressing
them at registers 0 through 0FH of the Attribute Controller. However,
setting the palette registers is a bit tricky—bit 5 of the Attribute
Controller Index register must be 0 while the palette registers are
written to, and glitches can occur if the updating doesn’t take place
during the blanking interval—and besides, it turns out that there’s no
written to, and glitches can occur if the updating doesn't take place
during the blanking interval—and besides, it turns out that there's no
need at all to go straight to the hardware on this one. Conveniently,
the EGA BIOS provides us with video function 10H, which supports setting
either any one palette register or all 16 palette registers (and the
@ -21,7 +21,7 @@ to. If AL is 1 (subfunction 1), then BH contains the value to set the
overscan (border) color to. Finally, if AL is 2 (subfunction 2), then
ES:DX points to a 17-byte array containing the values to set palette
registers 0-15 and the overscan register to. (For completeness, although
it’s unrelated to the palette registers, there is one more subfunction
it's unrelated to the palette registers, there is one more subfunction
of video function 10H. If AL = 3 (subfunction 3), bit 0 of BL is set to
1 to cause bit 7 of text attributes to select blinking, or set to 0 to
cause bit 7 of text attributes to select highreverse video.)
@ -44,16 +44,16 @@ produce high-intensity colors. Palette register 6 is set to 14H to
produce brown, rather than the yellow that the expected value of 6H
would produce.)
When you run Listing 29.3, you’ll see that the whole screen changes
When you run Listing 29.3, you'll see that the whole screen changes
color as each new color set is selected. This occurs because most of the
pixels on the screen have a value of 0, selecting the background color
stored in palette register 0, and we’re reprogramming palette register 0
stored in palette register 0, and we're reprogramming palette register 0
right along with the other 15 palette registers.
It’s important to understand that in Listing 29.3 the contents of
It's important to understand that in Listing 29.3 the contents of
display memory are never changed after initialization. The only change
is the mapping from the 4-bit pixel data coming out of display memory to
the 6-bit data going to the monitor. For this reason, it’s technically
the 6-bit data going to the monitor. For this reason, it's technically
inaccurate to speak of bits in display memory as representing colors;
more accurately, they represent attributes in the range 0-15, which are
mapped to colors 0-3FH by the palette registers.
@ -61,7 +61,7 @@ mapped to colors 0-3FH by the palette registers.
**LISTING 29.3 L29-3.ASM**
; Program to illustrate the color mapping capabilities of the
; EGA’s palette registers.
; EGA's palette registers.
;
VGA_SEGMENT equ 0a000h
SC_INDEX equ 3c4h ;Sequence Controller Index register
@ -70,16 +70,16 @@ mapped to colors 0-3FH by the palette registers.
TOP_BAR equ BAR_HEIGHT*6 ;start the bars down a bit to
; leave room for text
;
stack segment para stack ‘STACK’
stack segment para stack ‘STACK'
db 512 dup (?)
stack ends
;
Data segment word ‘DATA’
KeyMsg db ‘Press any key to see the next color set. ’
db ‘There are 64 color sets in all.’
Data segment word ‘DATA'
KeyMsg db ‘Press any key to see the next color set. '
db ‘There are 64 color sets in all.'
db 0dh, 0ah, 0ah, 0ah, 0ah
db 13 dup (‘ ’), ‘Attribute’
db 38 dup (‘ ’), ‘Color$’
db 13 dup (‘ '), ‘Attribute'
db 38 dup (‘ '), ‘Color$'
;
; Used to label the attributes of the color bars.
;
@ -87,27 +87,27 @@ mapped to colors 0-3FH by the palette registers.
x= 0
rept 16
if x lt 10
db ‘0’, x+‘0’, ‘h’, 0ah, 8, 8, 8
db ‘0', x+‘0', ‘h', 0ah, 8, 8, 8
else
db ‘0’, x+‘A’-10, ‘h’, 0ah, 8, 8, 8
db ‘0', x+‘A'-10, ‘h', 0ah, 8, 8, 8
endif
x= x+1
endm
db ‘$’
db ‘$'
;
; Used to label the colors of the color bars. (Color values are
; filled in on the fly.)
;
ColorNumberslabelbyte
rept 16
db ‘000h’, 0ah, 8, 8, 8, 8
db ‘000h', 0ah, 8, 8, 8, 8
endm
COLOR_ENTRY_LENGTHequ($-ColorNumbers)/16
db ‘$’
db ‘$'
;
CurrentColordb?
;
; Space for the array of 16 colors we’ll pass to the BIOS, plus
; Space for the array of 16 colors we'll pass to the BIOS, plus
; an overscan setting of black.
;
ColorTable db 16 dup (?), 0
@ -133,9 +133,9 @@ mapped to colors 0-3FH by the palette registers.
int 21h
;
; Put up the color bars, one in each of the 16 possible pixel values
; (which we’ll call attributes).
; (which we'll call attributes).
;
mov cx,16 ;we’ll put up 16 color bars
mov cx,16 ;we'll put up 16 color bars
sub al,al ;start with attribute 0
BarLoop:
push ax
@ -259,10 +259,10 @@ mapped to colors 0-3FH by the palette registers.
BinToHexDigit proc near
cmp al,9
ja IsHex
add al,‘0’
add al,‘0'
ret
IsHex:
add al,‘A’-10
add al,‘A'-10
ret
BinToHexDigit endp
;
@ -281,7 +281,7 @@ mapped to colors 0-3FH by the palette registers.
mov al,[CurrentColor] ;start with the current color
mov bx,offset ColorNumbers+1
;build color number text string on the fly
mov cx,16 ;we’ve got 16 colors to do
mov cx,16 ;we've got 16 colors to do
ColorNumberLoop:
pus hax;save the color #
and al,3fh;limit to 6-bit color values