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98 lines
3.5 KiB
Markdown
98 lines
3.5 KiB
Markdown
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[← Home](../../README.md) · [Hardware](../README.md) · [ECS](README.md)
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# ECS Productivity & Multiscan Display Modes
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## Overview
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ECS introduces **BEAMCON0** which allows the Amiga to produce non-standard display timings. The most useful are **productivity mode** (~28 kHz / 31 kHz horizontal) and **multiscan mode**, which provide flicker-free, high-resolution displays compatible with standard SVGA monitors.
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These modes are available on A3000 and some A2000/A600 configurations with a multisync monitor.
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## Standard OCS Timings (for reference)
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| Mode | H rate | V rate | Resolution |
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|---|---|---|---|
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| PAL LORES | 15.625 kHz | 50 Hz | 320×256 |
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| PAL HIRES | 15.625 kHz | 50 Hz | 640×256 |
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| NTSC LORES | 15.720 kHz | 60 Hz | 320×200 |
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| NTSC HIRES | 15.720 kHz | 60 Hz | 640×200 |
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| PAL interlace | 15.625 kHz | 50 Hz (25 Hz/field) | 320×512 / 640×512 |
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## ECS Multiscan Modes
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| Mode | H rate | V rate | Resolution | BEAMCON0 |
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|---|---|---|---|---|
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| Productivity | ~28.6 kHz | 57 Hz | 640×480 | $0A00 |
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| Super72 | ~28.6 kHz | 72 Hz | 800×600 (approx) | varies |
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| DblPAL | 31.25 kHz | 50 Hz | 640×512 | custom |
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| DblNTSC | 31.47 kHz | 60 Hz | 640×400 | custom |
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| VGA-like | 31.47 kHz | 60 Hz | 640×480 | custom |
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## Programming Productivity Mode
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Productivity mode on the A3000 (PAL, 640×480):
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```asm
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; Set BEAMCON0 for variable beam timing
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move.w #$0A00, $DFF1DC ; VARBEAMEN | VARVSYEN
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; Program horizontal total, sync, blank (custom timing)
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move.w #$71, $DFF1C0 ; HTOTAL (horizontal total - 1)
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move.w #$0F, $DFF1C4 ; HSSTRT (H sync start)
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move.w #$19, $DFF1C6 ; HSSTOP (H sync stop)
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move.w #$09, $DFF1C8 ; HBSTRT (H blank start)
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move.w #$71, $DFF1CA ; HBSTOP (H blank stop)
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; Vertical timing
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move.w #$0242, $DFF1E0 ; VTOTAL
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move.w #$0015, $DFF1E6 ; VSSTRT
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move.w #$001D, $DFF1E8 ; VSSTOP
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```
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> [!NOTE]
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> The exact register values depend on the target monitor's sync requirements. The A3000's monitor (1084S or Commodore 1950) has a specific timing window. Always consult the monitor's datasheet.
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## OS Support: ScreenModes
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AmigaOS 3.1 integrates ECS productivity modes through the **screenmode** system:
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```c
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#include <graphics/modeid.h>
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#include <libraries/asl.h>
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/* Open a 640×480 productivity screen */
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struct Screen *scr = OpenScreenTags(NULL,
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SA_DisplayID, PRODDBL_MONITOR_ID | HIRES_KEY,
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SA_Width, 640,
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SA_Height, 480,
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SA_Depth, 4,
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TAG_DONE);
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```
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**Key mode IDs for ECS:**
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```c
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#define MULTISCAN_MONITOR_ID 0x00041000 /* multiscan / productivity */
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#define SUPER72_MONITOR_ID 0x00081000
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#define DBLNTSC_MONITOR_ID 0x00401000
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#define DBLPAL_MONITOR_ID 0x00421000
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```
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These IDs are returned by `BestModeID()` and accepted by `OpenScreen()` / `OpenScreenTags()`.
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## Hardware Requirements
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- **ECS chipset** (Super Agnus + ECS Denise) — required for BEAMCON0
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- **Multisync monitor** — standard 15 kHz PAL/NTSC monitors do not support 31 kHz
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- **A3000** — has built-in multiscan support; A2000 requires a separate scan doubler card
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## Flicker Fixer (A2000/A500)
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Some Zorro II cards (e.g., Flicker Fixer by MicroWay, Indivision ECS) scan-double the 15 kHz signal to 31 kHz for use with VGA monitors. These operate transparently — no BEAMCON0 programming needed.
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## References
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- ADCD 2.1 Hardware Manual — ECS display modes
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- AmigaMail Vol. 2 — ECS multiscan articles
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- NDK39: `graphics/modeid.h` — monitor mode IDs
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- A3000 Technical Reference Manual — display timing chapter
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