Editing IBM Monochrome Display Adapter

{{Infobox computer peripheral
| name          = IBM Monochrome Display Adapter
| image         = [[File:IBM MDA card.jpg|260px]]
| caption       = IBM PC Original Monochrome Display and Parallel Printer Adapter (MDA)
| manufacturer  = IBM
| type          = 8-bit ISA video display adapter (text only) with integrated parallel printer port
| release_date  = 1981 (with the original IBM PC)
| interface     = 8-bit ISA
| compatible    = [[IBM PC (5150)]], [[IBM PC XT (5160)]], [[IBM PC AT (5170)]], PC-compatible clones
| connectivity  = DB-9 TTL monochrome (drives the [[IBM 5151]]); DB-25 Centronics parallel (LPT1)
}}

The '''IBM Monochrome Display Adapter''' ('''MDA''') is the original 8-bit ISA monochrome text adapter IBM released alongside the [[IBM PC (5150)]] in 1981. Unlike the [[IBM Color Graphics Adapter|CGA]], the MDA has '''no graphics modes''' — it produces only 80 × 25 text in a 9 × 14 character cell — but the larger cell yields a 720 × 350-pixel image that is noticeably crisper for office work. The card also carries the IBM PC's '''parallel printer port''' on its back-panel DB-25 connector, an idiosyncratic combination that means removing the MDA also removes the printer port.

== Hardware ==

* '''Motorola MC6845 CRTC''' — same timing chip as CGA, programmed for 18.432 kHz horizontal / 50 Hz vertical.
* '''4 KB video RAM.'''
* '''Character ROM''' carrying the IBM MDA font in a 9 × 14 cell.
* '''TTL output''' on DB-9 (drives the [[IBM 5151]]).
* '''Centronics parallel port''' on DB-25 — LPT1 by default.

== Video Mode ==

* Mode 7 — 80 × 25 text, monochrome.
* Per-character attribute byte selects: normal, bright, underline, reverse video, blink, invisible.
* No graphics mode.

== Common Faults ==

* '''No video, beep code 1 long + 2 short''' — reseat the MDA card first.
* '''Garbled text''' — bad character ROM. Replace with a known-good donor.
* '''Missing or duplicated columns''' — bad VRAM chip.
* '''Smoke from a tantalum''' — replace the failed tantalum.
* '''Printer port dead but video fine''' — the 74-series latch or buffer on the parallel side has failed.

== Hercules Compatibility ==

The Hercules Graphics Card from Hercules Computer Technology (1982) added 720 × 348 graphics on top of MDA's text mode. A genuine IBM MDA does '''not''' have these graphics modes — it is text-only.

== References ==

* [https://en.wikipedia.org/wiki/IBM_Monochrome_Display_Adapter IBM Monochrome Display Adapter — Wikipedia].
* [https://www.seasip.info/VintagePC/mda.html Monochrome Display Adapter Notes], Seasip.info.

== Related Pages ==

* [[IBM PC (5150)]]
* [[IBM 5151]]
* [[IBM Color Graphics Adapter]]
* [[IBM PC (5150) Capacitor Replacement Guide]]

[[Category:IBM]]