This project is part of a tutorial from http://emulator101.com/
DDD - Destination SSS - Src
111 - A 000 - B 001 - C 010 - D 011 - E 100 - H 101 - L
110 - Memory
00 - B-C 01 - D-E 10 - H-L 11 - SP
MOV r1, r2 0 1 D D D S S S
The following is some notes on memory mapping from https://www.emutalk.net/threads/space-invaders.38177/
Code: Space Invaders, (C) Taito 1978, Midway 1979
CPU: Intel 8080 @ 2MHz (CPU similar to the (newer) Zilog Z80)
Interrupts: $cf (RST 8) at the start of vblank, $d7 (RST $10) at the end of vblank.
Video: 256(x)*224(y) @ 60Hz, vertical monitor. Colours are simulated with a plastic transparent overlay and a background picture. Video hardware is very simple: 7168 bytes 1bpp bitmap (32 bytes per scanline).
Sound: SN76477 and samples.
Memory map: ROM $0000-$07ff: invaders.h $0800-$0fff: invaders.g $1000-$17ff: invaders.f $1800-$1fff: invaders.e
RAM
$2000-$23ff: work RAM
$2400-$3fff: video RAM
$4000-: RAM mirror
Ports: Read 1 BIT 0 coin (0 when active) 1 P2 start button 2 P1 start button 3 ? 4 P1 shoot button 5 P1 joystick left 6 P1 joystick right 7 ?
Read 2
BIT 0,1 dipswitch number of lives (0:3,1:4,2:5,3:6)
2 tilt 'button'
3 dipswitch bonus life at 1:1000,0:1500
4 P2 shoot button
5 P2 joystick left
6 P2 joystick right
7 dipswitch coin info 1:off,0:on
Read 3 shift register result
Write 2 shift register result offset (bits 0,1,2)
Write 3 sound related
Write 4 fill shift register
Write 5 sound related
Write 6 strange 'debug' port? eg. it writes to this port when
it writes text to the screen (0=a,1=b,2=c, etc)
(write ports 3,5,6 can be left unemulated, read port 1=$01 and 2=$00
will make the game run, but but only in attract mode)
I haven't looked into sound details.
16 bit shift register: f 0 bit xxxxxxxxyyyyyyyy
Writing to port 4 shifts x into y, and the new value into x, eg.
$0000,
write $aa -> $aa00,
write $ff -> $ffaa,
write $12 -> $12ff, ..
Writing to port 2 (bits 0,1,2) sets the offset for the 8 bit result, eg.
offset 0:
rrrrrrrr result=xxxxxxxx
xxxxxxxxyyyyyyyy
offset 2:
rrrrrrrr result=xxxxxxyy
xxxxxxxxyyyyyyyy
offset 7:
rrrrrrrr result=xyyyyyyy
xxxxxxxxyyyyyyyy
Reading from port 3 returns said result.
Overlay dimensions (screen rotated 90 degrees anti-clockwise): ,___________________________. |WHITE ^ | | 32 | | v | |-------------------------------| |RED ^ | | 32 | | v | |-------------------------------| |WHITE | | < 224 > | | | | ^ | | 120 | | v | | | | | | | |-------------------------------| |GREEN | | ^ ^ | |56 ^ 56 | | v 72 v | | v ______________| | ^ | | ^ | |<16> | < 118 > |16 < 122 > | | v | | v | |WHITE| | WHITE| `-------------------------------'
Way of out of proportion :P