IBM PCjr

From: Captain Napalm <spc_at_armigeron.com>
Date: Mon Jun 23 20:59:33 1997

It was thus said that the Great Marvin once stated:
>
> SUPRDAVE_at_aol.com wrote:
> >
> > standard cga monitor into the back. if anyone's interested, i could post the
> > pinouts of the dongle so you can use cga. the last hamfest i went to have
>
> As I recall, the PC Jr. does not use CGA but rather EGA. Something in
> the back of my mind says that the REAL PC Jr. monitor is not quite EGA
> but definetely better than CGA.

  It supports two modes that CGA doesn't: 320x200 16 color and 640x200 4
color, in addition to the other CGA modes. The 320x200 16 mode isn't quite
EGA in layout though - the palette registers only support 2 bits of red, 2
of green and 2 of blue, and the layout of the pixels follows (more or less)
the CGA standard than the EGA bitplanes.

  Each byte held two pixels (four bits per pixel) and the memory layout was:

0x0000: 2000 bytes of screen information, each line 40 bytes, lines
                evenly divisible by 0

0x2000: 2000 bytes of screen information, each line 40 bytes,
                line % 4 == 1

0x4000: 2000 bytes of screen information, each line 40 bytes,
                line % 4 == 2

0x6000: 2000 bytes of screen information, each line 40 bytes,
                line % 4 == 3

  The 620x200 4 color mode was similarly laid (layed?) out, only there were
four pixels per byte (2 bits per pixel).

  -spc (Although with proper programming, the CGA could support 160x100
        16 colors (or was it 160x200?))
Received on Mon Jun 23 1997 - 20:59:33 BST