From:	Till Harbaum <harbaum AT ra DOT ibr DOT cs DOT tu-bs DOT de>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: vertical retrace and LCD screens
Date:	07 Feb 1997 11:21:28 +0100
Organization:	TU Braunschweig, Informatik (Bueltenweg), Germany
Lines:	33
Sender:	harbaum AT kastor
Distribution:	world
Message-ID:	<ykswwskyl07.fsf@ra.ibr.cs.tu-bs.de>
References:	<5daceq$sci AT cymbal DOT cs DOT indiana DOT edu>
NNTP-Posting-Host:	kastor.ibr.cs.tu-bs.de
To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp

> I've been cleaning up some graphical routines I've written in allegro,
> and one thing I've considered is using vsync() to do some drawing during
> the "vertical retrace".  But I'm working on a notebook, which means an
> LCD screen instead of a CRT.  Is there something analogous to a vertical
> retrace with LCDs?  I'm familiar with CRTs, but LCD displays are still
> new to me.

Most VGAs don't toggle the interrupt line (irq9 is for vsync, if i remember
right) so most programs simply wait for the vsync bit in a vga register 
to toggle. most flat panel displays (tfts, passive single scan lcds, plasma,
el) use a display technique very similar to crts. They start drawing at left 
upper corner and get right/down till they reach the lower right corner and
then clear all counters to return to the upper left corner. This equals
a crts vsync (but it's called flm at most flat panels). In fact all pc
compatible notebooks with vga graphics have to implement the whole vga
register set and therefore implement the vsync bit, too. 

For further information read something like:

65535 High Performance Flat Panel / CRT VGA Controller Data Sheet, Chips & Technologies Inc., March 1994
65540/545 High Performance Flat Panel / CRT VGA Controllers Data Sheet, Chips & Technologies Inc., May 1994
65548 High Performace Flat Panel / CRT GUI Accelerator Data Sheet, Revision 0.9, Chips & Technologies Inc., May 1995
CL-GD62XX Single DRAM LCD/VGA Controllers Preliminary Data Book, Cirrus Logic, Oktober 1993
CL-GD6440 High Resolution VGA LCD Controller Data Book, Cirrus Logic, Juni 1994
WD90C24A/A2 Windows Accelerated High-Resolution VGA LCD Controller for Low Power Applications Data Book, Western Digital Corp., 1994
Toshiba Color TFT-LCD Module LTM10CO15K Data Sheet, Systemelektronik GmbH, Braunschweig, germany
Device Specification for Sharp TFT-LCD Module Model No. LQ10D021, REIN Components, Nettetal, germany
Samsung LT104V3-102 Users Handbook, Samsung Semiconductors

Ciao,
  Till

T DOT Harbaum AT tu-bs DOT de

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