AST RESEARCH, INC.        TECHNICAL BULLETIN # 1401          7-12-96 



TITLE: Ascentia External Monitor Flicker


SUMMARY

   An external monitor, connected to an Ascentia 950N or an Ascentia P
   system through the external video port, may experience noticeable 
   flicker.

   This issue applies to all the Ascentia 950N and Ascentia P systems.


ISSUE

   When an external monitor is attached to the external video port on
   the Ascentia system in simultaneous video mode, there may be 
   noticeable flicker on the monitor.  When the unit is set for 
   external video mode, the monitor image appears to be flicker-free.


BACKGROUND

   If the unit is configured to operate in simultaneous video mode, 
   the VGA controller in the Ascentia system must generate 
   signals that are compatible with the internal display panel.  
   If the Ascentia has a Dual Scan STN display, the external 
   video will be 800 x 600, with a vertical refresh rate of 53 Hz.  
   If the Ascentia is equipped with a TFT display, the external 
   video will be 800 x 600 with a vertical refresh rate of 60 Hz.

   Screen flicker will usually result on a CRT-based monitor with 
   vertical refresh frequencies of 53 and 60 Hz.  The LCD panels used
   in  portable computers operate much differently than CRT devices, 
   and therefore do not exhibit any type of flicker at the lower 
   refresh rates they require.


ACTION

   If the external monitor flicker is excessive, set the unit to 
   operate in external video mode only.  When operated in external 
   video mode, the video controller circuitry in the Ascentia 
   functions the same way as a standard SVGA controller, with vertical
   refresh rates of up to 75 Hz., depending on video mode and driver 
   support. 


NOTES

   N/A

TAN 009323RH and 001226JP

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