IBM Options and Adapters - IBM Monochrome Display and Printer Adapter
The IBM Monochrome Display and Printer Adapter section of IBM's Options and Adapters technical reference is the manufacturer's own reference for the card usually called MDA.
What it contains
[edit | edit source]- Monochrome display adapter function — the Motorola 6845 CRT controller, 4 KB of display-buffer RAM with no parity, the dual-port buffer, the two-bytes-in-553 ns fetch giving 1.8 MB/s, the 8 KB character generator holding 256 character codes, the 9 PEL by 14 PEL character box carrying a 7 PEL by 9 PEL character, the 18 kHz monitor requirement, and the statement that the adapter does not support a light pen when used with a P39-phosphor display.
- Programming — the 6845 register set, the mode-control register at hex 3B8 and the status port at hex 3BA.
- Connector specifications — the 9-pin display connector with pins 1 and 2 ground, pins 3 to 5 unused, pin 6 +Intensity, pin 7 +Video, pin 8 +Horizontal and pin 9 −Vertical, at 0.0 to 0.6 Vdc down level and +2.4 to 3.5 Vdc up level.
- Printer adapter function — the 12 latched TTL output points and 5 steady-state input points, the register map and the DB-25 connector assignments.
- Logic diagrams — full schematics for both halves of the card.
Download it here: IBM Options and Adapters - IBM Monochrome Display and Printer Adapter.pdf