To:         All Federal Users at Federal
From:       Strang
Subject:    1537 & VGA screen limitations
Date sent:  09/28/89 12:09 PM


Here is some information about the 1537 display and the 1500 VGA upgrade display that may not be obvious at first glance.  Neither of these displays supports the 640x400 monochrome display mode (AT&T or Toshiba mode) that we have grown used to in the GRiDCase 1500s.  The new display controller chips in both cases support VGA (640x480, 16 color), EGA (640x350, 16 color), and CGA (640x200, 2 color, or 4 color in text mode), resolution and that's all.

The 1537 supports EGA and CGA resolution on the internal display, and VGA on an external monitor.  Note that while the 1537 has a 640x400 pixel internal display, NONE of it's display modes allow all those pixels to be addresses independently.  The highest pixel resolution accessable in software is EGA, which is 640x350.  You may ask "Why the extra 50 pixels, then?  It's because in CGA mode, the display works like the present 1500 display, in mapping every CGA pixel to 2 screen pixels vertically, for a total of 400.  This is sometimes call "double scan".  While EGA allows 16 colors, the 1537 internal display will, at last report, provide only 4 usable shades, like the present 1500 display does.

The 1500 VGA upgrade supports VGA, EGA, and CGA resolutions, both on the internal display and on an external monitor.  It does not support 640x400.  I don't know how many usable shades this internal display will provide.

The 3 main impacts I see from this situation are:

1) Software customized to support the 640x400 display mode will not work in that mode on these displays.  Hopefully, the software will support VGA and/or EGA, so users will not have to drop back to CGA resolution.  For any software that only supports 640x400, software modifications will be necessary.

2) 1537 customers may well have made the assumption that they can address all the pixels on the 640x400 screen, when in fact they can only address up to 640x350.

3) InteGRiD will come up in CGA mode on both these displays, despite thet availability of lots more pixels on the display.

Will