← Home · Hardware · OCS
OCS Custom Register Map
Base address: $00DFF000. All registers are 16-bit (word) wide. Byte access is valid for the appropriate byte lane.
Legend: R = read, W = write, RW = read-write, S = strobe (write triggers action)
DMA and Interrupt Control
| Offset |
Name |
Dir |
Description |
| $002 |
DMACONR |
R |
DMA control register (read) |
| $01C |
INTENAR |
R |
Interrupt enable (read) |
| $01E |
INTREQR |
R |
Interrupt request (read) |
| $096 |
DMACON |
W |
DMA control (write: bit15=SET/CLR) |
| $09A |
INTENA |
W |
Interrupt enable (write: bit15=SET/CLR) |
| $09C |
INTREQ |
W |
Interrupt request — ack / force |
Beam Position (Read Only)
| Offset |
Name |
Dir |
Description |
| $004 |
VPOSR |
R |
Vertical position high, LOF bit |
| $006 |
VHPOSR |
R |
Vertical + horizontal beam position |
| $007 |
VHPOS |
R |
Horizontal beam position (byte) |
Copper
| Offset |
Name |
Dir |
Description |
| $02E |
COPCON |
W |
Copper control (CDANG bit) |
| $080 |
COP1LCH |
W |
Copper list 1 pointer high |
| $082 |
COP1LCL |
W |
Copper list 1 pointer low |
| $084 |
COP2LCH |
W |
Copper list 2 pointer high |
| $086 |
COP2LCL |
W |
Copper list 2 pointer low |
| $088 |
COPJMP1 |
S |
Restart Copper from list 1 |
| $08A |
COPJMP2 |
S |
Restart Copper from list 2 |
| $08C |
COPINS |
W |
Copper instruction (direct write) |
| $000 |
BLTDDAT |
R |
Blitter dest early read (Copper use) |
Blitter
| Offset |
Name |
Dir |
Description |
| $040 |
BLTCON0 |
W |
Blitter control 0 (minterm, channels) |
| $042 |
BLTCON1 |
W |
Blitter control 1 (line mode, fill) |
| $044 |
BLTAFWM |
W |
First word mask, channel A |
| $046 |
BLTALWM |
W |
Last word mask, channel A |
| $048 |
BLTCPTH |
W |
Channel C pointer high |
| $04A |
BLTCPTL |
W |
Channel C pointer low |
| $04C |
BLTBPTH |
W |
Channel B pointer high |
| $04E |
BLTBPTL |
W |
Channel B pointer low |
| $050 |
BLTAPTH |
W |
Channel A pointer high |
| $052 |
BLTAPTL |
W |
Channel A pointer low |
| $054 |
BLTDPTH |
W |
Destination pointer high |
| $056 |
BLTDPTL |
W |
Destination pointer low |
| $058 |
BLTSIZE |
W |
Blitter size + start (height×64 + width) |
| $060 |
BLTCMOD |
W |
Channel C modulo |
| $062 |
BLTBMOD |
W |
Channel B modulo |
| $064 |
BLTAMOD |
W |
Channel A modulo |
| $066 |
BLTDMOD |
W |
Destination modulo |
| $070 |
BLTCDAT |
W |
Channel C data register |
| $072 |
BLTBDAT |
W |
Channel B data register |
| $074 |
BLTADAT |
W |
Channel A data register |
Bitplane Pointers
| Offset |
Name |
Dir |
Description |
| $0E0 |
BPL1PTH |
W |
Bitplane 1 pointer high |
| $0E2 |
BPL1PTL |
W |
Bitplane 1 pointer low |
| $0E4 |
BPL2PTH |
W |
Bitplane 2 pointer high |
| $0E6 |
BPL2PTL |
W |
Bitplane 2 pointer low |
| $0E8 |
BPL3PTH |
W |
Bitplane 3 pointer high |
| $0EA |
BPL3PTL |
W |
Bitplane 3 pointer low |
| $0EC |
BPL4PTH |
W |
Bitplane 4 pointer high |
| $0EE |
BPL4PTL |
W |
Bitplane 4 pointer low |
| $0F0 |
BPL5PTH |
W |
Bitplane 5 pointer high |
| $0F2 |
BPL5PTL |
W |
Bitplane 5 pointer low |
| $0F4 |
BPL6PTH |
W |
Bitplane 6 pointer high |
| $0F6 |
BPL6PTL |
W |
Bitplane 6 pointer low |
Bitplane Control
| Offset |
Name |
Dir |
Description |
| $100 |
BPLCON0 |
W |
Bitplane control 0 (depth, HAM, HIRES, LACE) |
| $102 |
BPLCON1 |
W |
Bitplane scroll (fine scroll values) |
| $104 |
BPLCON2 |
W |
Sprite vs bitplane priority |
| $108 |
BPL1MOD |
W |
Bitplane modulo (odd planes) |
| $10A |
BPL2MOD |
W |
Bitplane modulo (even planes) |
| $110 |
BPL1DAT |
W |
Bitplane 1 data register |
| $112 |
BPL2DAT |
W |
Bitplane 2 data register |
| $114 |
BPL3DAT |
W |
Bitplane 3 |
| $116 |
BPL4DAT |
W |
Bitplane 4 |
| $118 |
BPL5DAT |
W |
Bitplane 5 |
| $11A |
BPL6DAT |
W |
Bitplane 6 |
BPLCON0 bit layout:
bit 15: HIRES (1 = 640 pixel wide)
bit 14-12: BPU2-0 (number of bitplanes: 0–6)
bit 11: HAM (1 = Hold-And-Modify mode)
bit 10: DPF (dual playfield)
bit 9: COLOR (0 = monochrome, 1 = color)
bit 8: GAUD (genlock audio)
bit 7-4: (various, OCS = 0)
bit 1: ERSY (external sync)
bit 0: ECSENA (ECS enable — must be 0 on OCS)
Display Window and Fetch
| Offset |
Name |
Dir |
Description |
| $08E |
DIWSTRT |
W |
Display window start (V and H start) |
| $090 |
DIWSTOP |
W |
Display window stop |
| $092 |
DDFSTRT |
W |
Display data fetch start |
| $094 |
DDFSTOP |
W |
Display data fetch stop |
Sprite Pointers and Data
| Offset |
Name |
Dir |
Description |
| $120 |
SPR0PTH |
W |
Sprite 0 pointer high |
| $122 |
SPR0PTL |
W |
Sprite 0 pointer low |
| ... |
... |
|
Sprites 1–7 follow at +4 each |
| $13E |
SPR7PTL |
W |
Sprite 7 pointer low |
| $140 |
SPR0POS |
W |
Sprite 0 position |
| $142 |
SPR0CTL |
W |
Sprite 0 control |
| $144 |
SPR0DATA |
W |
Sprite 0 image data word A |
| $146 |
SPR0DATB |
W |
Sprite 0 image data word B |
| ... |
|
|
Sprites 1–7 follow |
| $178 |
SPR7DATB |
W |
Sprite 7 image data word B |
Audio Registers
| Offset |
Name |
Dir |
Description |
| $0A0 |
AUD0LCH |
W |
Audio ch 0 pointer high |
| $0A2 |
AUD0LCL |
W |
Audio ch 0 pointer low |
| $0A4 |
AUD0LEN |
W |
Audio ch 0 length (words) |
| $0A6 |
AUD0PER |
W |
Audio ch 0 period (clock divider) |
| $0A8 |
AUD0VOL |
W |
Audio ch 0 volume (0–64) |
| $0AA |
AUD0DAT |
W |
Audio ch 0 data (direct, non-DMA) |
| ... |
|
|
Channels 1–3 follow at +$10 |
Serial Port
| Offset |
Name |
Dir |
Description |
| $030 |
SERDAT |
W |
Serial data and stop bits |
| $018 |
SERDATR |
R |
Serial data receive and status |
| $032 |
SERPER |
W |
Serial period and word length |
Disk DMA
| Offset |
Name |
Dir |
Description |
| $020 |
DSKPTH |
W |
Disk pointer high |
| $022 |
DSKPTL |
W |
Disk pointer low |
| $024 |
DSKLEN |
W |
Disk length and write flag |
| $010 |
ADKCONR |
R |
Audio / disk control (read) |
| $09E |
ADKCON |
W |
Audio / disk control (write) |
| $07C |
DSKSYNC |
W |
Disk sync word |
Color Registers
| Offset |
Name |
Dir |
Description |
| $180 |
COLOR00 |
W |
Background / color 0 |
| $182 |
COLOR01 |
W |
Color 1 |
| ... |
|
|
|
| $1BE |
COLOR31 |
W |
Color 31 |
OCS colors: 12-bit RGB (4 bits per component, $0RGB format).
References
