pcjs/devices/pcx86/video/ibm/mda

layout	title	permalink
page	IBM Monochrome Display Adapter (MDA)	/devices/pcx86/video/ibm/mda/

IBM Monochrome Display Adapter (MDA)

IBM MDA Configurations

The easiest way for a machine to include an MDA Video component in its XML configuration file is to reference one of the project's predefined MDA configuration files, using the ref attribute; eg:

<video ref="/devices/pcx86/video/ibm/mda/ibm-mda.xml"/>

The referenced XML file automatically defines visual elements (eg, dimensions of the display window and other visual indicators), display behaviors (eg, touchscreen support, mouse pointer locking), and the character ROM to load.

Here's what ibm-mda.xml currently looks like:

<video id="videoMDA" screenWidth="1440" screenHeight="900" scale="true" smoothing="false" fontROM="/devices/pcx86/video/ibm/mda/ibm-mda.json" pos="center" padding="8px">
    <menu>
    <title>Monochrome Display</title>
    <control type="container" pos="right">
        <control type="led" label="Caps" binding="caps-lock" padleft="8px"/>
        <control type="led" label="Num" binding="num-lock" padleft="8px"/>
        <control type="led" label="Scroll" binding="scroll-lock" padleft="8px"/>
    </control>
    </menu>
</video>

The following IBM MDA configuration files are currently available:

• ibm-mda.xml
• ibm-mda-dual.xml

IBM MDA Character ROM

There is only one known MDA Character ROM (ibm-mda.json), and it is identical to the CGA Character ROM, because the ROM contains both the 8x14 MDA and 8x8 CGA fonts.

As documented in Video.doneLoad():

[T]here are TWO CGA fonts in the ROM: a thin 5x7 "single dot" font located at offset 0x1000, and a thick 7x7
"double dot" font at offset 0x1800.  The latter is the default font, unless overridden by a jumper setting on
the CGA card, so it is our default CGA font as well (although someday we may provide a virtual jumper setting
that allows you to select the thinner font).

For reference, here are the first 0x80 bytes at offset 0x1800 from this ROM, which contain the font data for the first 16 8x8 characters:

0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x7E,0x81,0xA5,0x81,0xBD,0x99,0x81,0x7E, // 0x00001800 ........~......~
0x7E,0xFF,0xDB,0xFF,0xC3,0xE7,0xFF,0x7E,0x6C,0xFE,0xFE,0xFE,0x7C,0x38,0x10,0x00, // 0x00001810 ~......~l...|8..
0x10,0x38,0x7C,0xFE,0x7C,0x38,0x10,0x00,0x38,0x7C,0x38,0xFE,0xFE,0xD6,0x10,0x38, // 0x00001820 .8|.|8..8|8....8
0x10,0x10,0x38,0x7C,0xFE,0x7C,0x10,0x38,0x00,0x00,0x18,0x3C,0x3C,0x18,0x00,0x00, // 0x00001830 ..8|.|.8........
0xFF,0xFF,0xE7,0xC3,0xC3,0xE7,0xFF,0xFF,0x00,0x3C,0x66,0x42,0x42,0x66,0x3C,0x00, // 0x00001840 ..........fBBf..
0xFF,0xC3,0x99,0xBD,0xBD,0x99,0xC3,0xFF,0x0F,0x07,0x0F,0x7D,0xCC,0xCC,0xCC,0x78, // 0x00001850 ...........}...x
0x3C,0x66,0x66,0x66,0x3C,0x18,0x7E,0x18,0x3F,0x33,0x3F,0x30,0x30,0x70,0xF0,0xE0, // 0x00001860 .fff..~.?3?00p..
0x7F,0x63,0x7F,0x63,0x63,0x67,0xE6,0xC0,0x18,0xDB,0x3C,0xE7,0xE7,0x3C,0xDB,0x18, // 0x00001870 .c.ccg..........