Cga And 6845 Emulation (Display) - Husky MP2500 Manual

The 80386EX microprocessor is an enhanced version of the 80386 and is
entirely compatible with it, executing all published instructions. The ROM
provides a BIOS that is (as far as practicable) IBM PC-compatible, with
extensions to use MP2500's special features; the BIOS is described in
section 18.2 and Chapters 20 to 30. These components will not be
described further here.
For pinouts and other interfacing information, see Appendix G.

31.4.1 CGA and 6845 emulation (display)

The colour graphics adaptor consists of 16 KByte of display memory and
seven registers:
Address Name
3D0 6845 index register (also at 3D2, 3D4 and 3D6)
3D1 6845 data register (also at 3D3, 3D5 and 3D7)
3D8 Mode control
3D9 Colour select
3DA Status
3DB Clear lightpen latch
3DC Preset lightpen latch
31.4.1.1 CGA RAM
The CGA RAM is 16 KByte from B8000H to BFFFFH. It is largely standard,
and will not be described further here, other than to remind you that on
MP2500, there is no display 'snow' problem, so programs need not wait for
the vertical retrace period before accessing the CGA RAM. (The only non-
standard aspect is that the 00H attribute byte (invisible) is not
implemented.)
Also note that while the MP2500 LCD can only display monochrome, all
colour and attribute bits are implemented in the CGA RAM, to ensure
compatibility.
296 H MP2500 System Developer's Guide
USKY