x86 programming for Ms Dos Computers in CGA , EGA and VGA

The IBM 8086 took the world by storm!

Although inferior to the 68000 - the x86 soon took over, and is the basis for all the computers we have today...

Starting with the 8086, and soon moving to the 286, 386 and so on... each iteration has added more commands and power, and along the way the PC has gained functionality...


In these tutorials, we'll take a look at the early  basic machines, and learn how we can use Assembly to write games that can be used in MSDos via DosBox!

We'll cover 3 graphics modes...

CGA 320x200 4 color (Cyan,Magenta,White or Green,Red,Yellow)
EGA 320x200 16 color fixed palette
VGA 320x200 256 color palette

Amstrad PC1512 IBM Compatible

If you want to learn 8086 get the Cheatsheet! it has all the 8086 commands, It will help you get started with ASM programming, and let you quickly look up commands when you get confused!

Useful Documents

MASM61PROGUIDE - Microsoft Assembler guide
MASM - Microsoft's Dos based assembler
80x86 IBM PC and Compatible Computers - Programming guide
8086/186 - Intel CPU manual

ChibiAkumas Tutorials

8086 Hello World Series

Lesson H1 - Hello World on MS Dos
Lesson H3 - Hello World on MS Dos via Native Tools (MASM 6.11) [DOS]

8086 Simple Samples

Lesson S1 - Sprite drawing and Simple key movement in MS DOS

8086 Platform Specific Lessons

Lesson P1 - Bitmap graphics on DOS with CGA [DOS]
Lesson P2 - Bitmap graphics on DOS with EGA [DOS]
Lesson P3 - Bitmap graphics on DOS with VGA [DOS]
Lesson P5 - Key reading in DOS [DOS]
Lesson P7 - Mouse reading in MS DOS
Lesson P8 - Beeper speaker on MS DOS! [DOS]
Lesson P9 - Adlib/Soundblaster sound with MS DOS! [DOS]

8086 SuckHunt Series

Lesson SuckShoot1 - Suck Shoot on the 8086 [DOS]
Lesson SuckShoot4 - Suck Shoot on the 8086 with CGA [DOS]

CGA color Palette


 Palette 0 Dark Palette 0
Bright		 Palette 1 Dark Palette 1 Bright
0



1



2



3




EGA color Palette

The EGA system uses 16 colors - it's 320x200 can only use a palette of 16 colors (the same colors!)

Each color has a logical number from 0-16, and a Hardware number (used for palette definitions) from 0-63

0 - 0 1 - 1 2 - 2 3 - 3 4 - 4 5 - 5 6 - 20 7 - 7
8 - 56 9 - 57 10 - 58 11 - 59 12 - 60 13 - 61 14 - 62 15 - 63

EGA Ports

Port AH AL Purpose
03C0h   
%--RGBrgb 00h Palette
03C0h %--RGBrgb 01h Palette
03C0h %--RGBrgb 02h Palette
03C0h %--RGBrgb 03h Palette
03C0h %--RGBrgb 04h Palette
03C0h %--RGBrgb 05h Palette
03C0h %--RGBrgb 06h Palette
03C0h %--RGBrgb 07h Palette
03C0h %--RGBrgb 08h Palette
03C0h %--RGBrgb 09h Palette
03C0h %--RGBrgb 0Ah Palette
03C0h %--RGBrgb 0Bh Palette
03C0h %--RGBrgb 0Ch Palette
03C0h %--RGBrgb 0Dh Palette
03C0h %--RGBrgb 0Eh Palette
03C0h %--RGBrgb 0Fh Palette
03C0h %----MMMM 10h Mode Control
03C0h %--OOOOOO 11h Overscan
03C0h %--DDPPPP 12h Color plane enable
03C0h %----PPPP 13h Horizontal panning
03C2h %IFFS---- 00h Input status 0 register
03C2h %VHBDCEc 01h Misc Output register
03C4h %------SA 00h Sequencer reset
03C4h %----CScD 01h Sequence clocking mode
03C4h %----3210 02h Write mask register plane n)
03C4h %----CCcc 03h Character map select
03C4h %-----OMA 04h Memory mode
03CAh %------PP
Graphics 2 position
03CCh %------PP
Graphics 1 position
03CEh %----3210 00h In Write mode 0 set bit according to 3CEh
03CEh %----3210 01h In Write mode 0 set bit according to 3CEh
03CEh %----3210 02h In Write mode 0 set bit according to 3CEh
03CEh %----3210 03h In Write mode 0 set bit according to 3CEh
03CEh %------PP 04h Read Bitplane register
03CEh %--CORFWW 05h Read/Write Mode
03CEh %----MMOG 06h Graphics Misc
03CEh %----3210 07h Ignore bitplane register
03CEh %BBBBBBBB 08h Bit mask register
03D4h %HHHHHHHH 00h CRTC Horizontal Total
03D4h %HHHHHHHH 01h CRTC Horizontal Display End
03D4h %HHHHHHHH 02h CRTC Start Horiz Blanking Register
03D4h %-CCHHHHH 03h CRTC End Horiz Blanking Register
03D4h %HHHHHHHH 04h CRTC Start Horiz Retrace Register
03D4h %DCCHHHHH 05h CRTC End Horiz Retrace Register
03D4h %VVVVVVVV 06h CRTC Vertical Blank Total
03D4h %---LSEDT 07h CRTC Overflow register
03D4h %---LLLLL 08h CRTC Preset Row Scan Register
03D4h %---LLLLL 09h CRTC Maximum scan line register
03D4h %---CCCCC 0Ah CRTC Cursor Start Reg
03D4h %-DDCCCCC 0Bh CRTC Cursor End Reg
03D4h %AAAAAAAA 0Ch CRTC Cursor Start Address High Reg
03D4h %AAAAAAAA 0Dh CRTC Cursor Start Address Low Reg
03D4h %CCCCCCCC 0Eh CRTC Cursor Location High Reg
03D4h %CCCCCCCC 0Fh CRTC Cursor Location Low Reg
03D4h %VVVVVVVV 10h CRTC Vertical Retrace Start Reg
03D4h %PPPPPPPP 11h CRTC Light Pen Low Register (Read)
03D4h %--ICVVVV 11h CRTC Vertical Retrace End Reg (Write)
03D4h %VVVVVVVV 12h CRTC Virtical Display End Register
03D4h %OOOOOOOO 13h CRTC Offset Register
03D4h %---UUUUU 14h CRTC Underline location Reg
03D4h %VVVVVVVV 15h CRTC Start Vert Blanking Register
03D4h %---VVVVV 16h CRTC End Vert Blanking Register
03D4h %RWBDCSHc 17h CRTC: Mode control register
03D4h %LLLLLLLL 18h CRTC: Line Compare Register
03DAh %--CCVLlR
Input Status 1 Register (Read)
03DAh %------OO
Feature Control Register (Write)

Screen Layouts


CGA is a 2bpp screen mode, it's memory is at B800:0000h

EGA use 4 bitplanes, it's address is A000:0000... to change the bitplanes we need to OUT to 03C4h

VGA is a 8bpp screen mode, it's memory is at A000:0000h



Bits
Screen Mode Bits per pixel Pixels per byte Address Plane Mask 7 6 5 4 3 2 1 0
CGA - 4 2 bpp 4 B800:0000h
b1 b0 b1 b0 b1 b0 b1 b0
EGA - 13 4 bitplanes 8 A000:0000h out 03c4h,0102h p0-b7 p0-b6 p0-b5 p0-b4 p0-b3 p0-b2 p0-b1 p0-b0
out 03c4h,0202h p1-b7 p1-b6 p1-b5 p1-b4 p1-b3 p1-b2 p1-b1 p1-b0
out 03c4h,0302h p2-b7 p2-b6 p2-b5 p2-b4 p2-b3 p2-b2 p2-b1 p2-b0
out 03c4h,0402h p3-b7 p3-b6 p3-b5 p3-b4 p3-b3 p3-b2 p3-b1 p3-b0
out 03c4h,0F02h All-b7 All-b6 All-b5 All-b4 All-b3 All-b2 All-b1 All-b0
VGA 8bpp 1 A000:0000h
b7 b6 b5 b4 b3 b2 b1 b0

Beeper Sound Ports

Port Modes Purpose Bits Notes
0040 RW PIT counter 0, counter divisor (XT, AT, PS/2) CCCCCCCC Send L/H Pair
0041 RW PIT counter 1, RAM refresh counter (XT, AT) CCCCCCCC Send L/H Pair
0042 RW PIT counter 2, cassette & speaker (XT, AT, PS/2) CCCCCCCC Send L/H Pair
0043 RW PIT mode port, control word register for counters 0-2 CCAAMMMS C=Counter select (0-2), A=counter Access, M=counter Mode (0-5), S=counter Style (0=16 bit 1=BCD)
0061 W PPI Programmable Peripheral Interface 8255 (XT only) ----PPST P= parity checks S=Speaker enable T=speaker Timer enable
0061 R KB controller port B control register (ISA, EISA) EETDPPST E=errors T=Timer D=Detect P= parity checks S=Speaker enable T=speaker Timer enable

Adlib OPL2 Registers

The ADLIB sound card usesd OPL2, which is also supported by the full SoundBlaster range, it uses a range of registers to make its sounds, each sound channel is formed by a combination of two Operators

NOTE: OPL3 doubled the number of registers, with an 'Advanced' set... for simplicity (and my sanity) we'll just be covering the basic OPL2 set, which are supported by OPL3 as well!

There are a total of up to 9 sound channels... each sound is the combination of two "OP signals"... we should set both to get a sound from a channel! How the OPs are combined is defined by bit 0 of registers C0h-C8h... see the pdf documents for more info.

Channel Signal 1 2 3 4 5 6 7
(Ryt)		 8
(Ryt)		 9
(Ryt)
OP1 Slot 1 Signal 1
2
3
7
8
9
13
14
15
OP2 Slot 2 Signal
4
5
6
10
11
12
16
17
18
Register settings
for slot		 20
21
22
28
29
2A
30
31
32

23
24
25
2B
2C
2D
33
34
35
40
41
42
48
49
4A
50
51
52

43
44
45
4B
4C
4D
53
54
55
60
61
62
68
69
6A
70
71
72

63
64
65
6B
6C
6D
73
74
75
80
81
82
88
89
8A
90
91
92

83
84
85
8B
8C
8D
93
94
95
E0
E1
E2
E8
E9
EA
F0
F1
F2

E3
E4
E5
EB
EC
ED
F3
F4
F5
Register settings for 
the channel		 A0 A1 A2 A3 A4 A5 A6 A7 A8
B0 B1 B2 B3 B4 B5 B6 B7 B8
C0 C1 C2 C3 C4 C5 C6 C7 C8

Channels 7,8,9 can be toggled as Rhythm effects by setting bit 5 of 0BDh to 1

In this mode bits 0-4 of 0BDh will 'fire' the effects... each effect uses some of the signal slots, the registers for this slot will need to be set up as usual

BDh  bits %DDRBSTCH   

R=Rhythm enabled (channel 7-9 no longer normal FM sound)

Bit / Rhythm sound
 OP / Signal Slots used
B=Bass 13 & 16
S=Snare 17
T=Tom 15
C=Cymbal 18
H=Hihat 14


Sound over time

The OPs define how the sound level changes over time... K-On and K-Off mimic the way piano keys work.. when the key is struck the sound will start (Attack), and fade slowly (Decay) to a constant tone (Sustain), when the key is lifted, it will fade quickly (Release)

Adlib OPL2 Registers and bits

Register Details Bits Details
01h Test --WDDDDD W=Wave select Enable (opl2) / D=Test Data
02h Timer 1 Setting 80-20.4us TTTTTTTT T=Timer
03h Timer 2 Setting 320-82 us TTTTTTTT T=Timer
04h Timer 1/2 control RMM---SS R=Reset M=Mask S=?
08h Speech Synth / Keyboard Split NoteSel CS------ C=CSM Speech synth mode / S=note Select
20h - 35h Multi / Key Scale Rate / EG-Type Tone / Vibrato / AM modulation AVEKMMMM A=AM V=VIB E=EG-Typ K=KSR M=Multiple
40h - 55h Total Level / Key Scale Level KKTTTTTT K=KeyScaleLevel T=Total Level (0=loud)
60h - 75h Decay Rate / Attack Rate AAAADDDD A=Attack (0=slow) D=Decay (0=slow)
88h - 95h Release Rate / Sustain Level SSSSRRRR S=Sustain (0=loud) R=Release (0=slow)
A0h - A8h F number FFFFFFFF F=Fnumber L
B0h - B8h Block / K-ON --KBBBFF F=Fnumber H B=Block K=K-on
BDh Rhythm mode (Chn 7-9) / Vibrato Depth / AM Depth DDRBSTCH D=Depth (AM/VIB) R=Rhythm
B=Bass(13,16) S=Snare(17) T=Tom(15) C=Cymbal(18) H=Hihat(14)
C0h - C8h FeedBack factor / C=Connection sine/fm ----FFFC F=Feedback C=Connection (Op combination mode)
E0h - F5h Wave Select ------WW WW=Wave Select




(Address port Read) Status Reg IFF----- I=IRQ F=Flag

Useful ADLIB docs:

yamaha_ymf262 - OPL3 Manual (Adlib Gold / SB16)
YM3812 - OPL2 Manual (adlib)
ym3625 - OPL(1) manual
Soundblaster - Soundblaster programming guide
Adlib Programming - Adlib programming guide