MDA ( English Monochrome Display Adapter ) is an IBM PC video adapter introduced in 1981 as a standard video adapter (along with a CGA ), as well as a standard for monitors connected to it. MDA was monochrome and supported only one text mode (80 columns for 25 lines; video mode 7), without graphic modes.
Text video modes with so many characters per line and lines on the screen were popular; the consequence of which is, for example, that the source code of the Linux kernel is formatted for this video mode.
For the image of the symbol, a 9 × 14 matrix of pixels was used , of which the visible part of the symbol was composed as 7 × 11, and the remaining pixels were used to form the empty space between rows and columns.
The standard MDA video adapter was based on the Motorola 6845 chip and is equipped with 4 KB of video memory . The scanning frequency was 50 Hz , and a display with a long-lasting luminescent powder was recommended for operation.
Each character could have the following attributes: invisible , underlined , normal , bright (bold), inverted and flashing . Some of these attributes could be combined, and, for example, you can get text consisting of bright (bold) and underlined characters.
Theoretically, the MDA screen resolution was 720 × 350 pixels. Such a number can be obtained by multiplying the width of one character (9 pixels) by the number of columns (80) and the height of the character (14 pixels) by the number of lines (25). However, the MDA video adapter was not able to address individual pixels, it worked in text mode, in which one of 256 characters could be placed in each familiarity. In MDA, code page CP437 was used . The images of the characters were stored in the video card ROM , and there was no possibility of their programmatic changes. The only way to draw a graphic image on the screen is to use ASCII or ANSI graphics . The codepage included pseudographic characters for drawing tables and frames.
The original expansion card, released by IBM, contained in addition to the MDA-video adapter a parallel port controller, and the full name of such a card was: “Monochrome Display and Printer Adapter” (MDPA) - a monochrome display and printer adapter. The use of such a card saved the owner of the computer from having to buy a separate expansion card to connect the printer.
Content
Specification
D-sub 9-pin (DE-9) connector on the video card. View of the pins from the plug-in connector.
five | one |
9 | 6 |
Conclusion | Description |
---|---|
one | Ground |
2 | Ground |
3 | Not used |
four | Not used |
five | Not used |
6 | Intensity |
7 | Mono Video (Monochrome Video) |
eight | Horizontal Sync |
9 | Vertical Sync |
Signal
Type of | Digital, TTL |
---|---|
Resolution | 720h × 350v |
Horizontal Frequency | 18.432 kHz |
Frame rate | 50 Hz |
Number of colors | one |
Color intensity | 2-4 [2] |
Rival Video Adapters
- For users who need to work with graphics and / or color images, IBM supplied the CGA video adapter , released at the same time as the MDA. The CGA video adapter was initially more expensive and was considered as a solution for the upper segment of the market, but the low resolution in text modes (compared to MDA) made the CGA less attractive for business users.
- The Hercules graphics card from Hercules Graphics Card (HGC), which was released in 1982, supported both MDA text mode and monochrome graphics mode. This video adapter could control the state of individual pixels on the screen and display a black and white image with a resolution of 720 × 348 pixels. The CGA could not provide this resolution in any of its modes, including monochrome. Thus, even without color image support, HGC allowed the use of black and white graphics and MDA-compatible text mode, which for many users was very attractive.
- Next, a version of the HGC + adapter (Hercules Plus) was released, which was distinguished by the presence of the character generator loading circuit into a separate RAM .
See also
- OGA - complements MDA with graphical capabilities.
Notes
- ↑ IBM Personal Computer Hardware Library: Technical Reference (Revised edition, 1983)
- ↑ In total, there were 4 combinations of intensity levels and video, but not all monitors displayed 4 levels of brightness.
Links
- Monochrome Display Adapter Notes (English)