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MDA/Hercules Support #34

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charlysan opened this issue Jul 9, 2023 · 0 comments

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charlysan commented Jul 9, 2023 •

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Introduction

The purpose of this issue is to start a discussion about MDA/Hercules implementation.

Requirements & specs

Specs

Feature	IBM MDA	Hercules Graphics Card (HGC)
Text Mode	80x25 characters (720x350 pixels)	80x25 characters (720x350 pixels)
Graphics Mode	None	720x348 pixels
Vertical Sync Frequency	50 Hz	50 Hz
Horizontal Sync Frequency	~18.432 kHz	~18.432 kHz
Signal Type	TTL Digital	TTL Digital

DB9 Pinout

Pin number	IBM MDA	Hercules Graphics Card (HGC)
Pin 1	Ground	Ground
Pin 2	Ground	Ground
Pin 3	Not connected	Not connected
Pin 4	Not connected	Not connected
Pin 5	Not connected	Not connected
Pin 6	Intensity	Intensity
Pin 7	Video	Video
Pin 8	Horizontal Sync	Horizontal Sync
Pin 9	Vertical Sync	Vertical Sync

Video - Intensity signals

Video	Intensity	Resulting 'colour'
0	0	Black
0	1	Dim
1	0	Normal
1	1	Bright

Docs:

Implementation

Hardware

We could connect Video to Rin, and Intensity to Gin for example.

What about 18 KHz support?

Software

TBD

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