[Gllug] Two Questions

[Andrew Farnsworth]

t.clarke wrote:

>Nix asked if TFT screens refresh in any way  !
>
>I have no idea whether a pixel stays switched 'on' or has to be constantly
>refreshed,  but presumably the electronics that receive and decode the
>analogue signal from the VGA card either:
>a) reswitch each pixel every time a new 'scan line' is received from the VGA
>   card, or
>b) are clever enough to recognise that a given pixel has not changed state from
>the previous scan-line and leave it alone  ??
>  
>
In general, a TFT screen will leave a pixel on as long as it's logic 
says to leave it on.  All TFT displays, internally, are digital and most 
will have an Analog to Digital (AD) converter in them to handle "normal" 
VGA signals.  The system keeps a model of the screen in "memory" and 
only changes those pixels that need to be changed.  Thus the pixel will 
stay on until it is specifically changed.  However, don't confuse this 
with "stays on so requires no power"... It still takes electricity to 
maintain that pixel in that state, at least until they finalize the 
development of static state LCD screens.  This is not that important 
anyway as the vast majority of the energy used in an LCD screen is for 
the backlighting.

>I noted that on a box at home with a particular 'old' vga card operating in
>'dumb' character mode (low res) the TFT screen will from time to time display
>slight fuzziness on some characters where individuals pixels at the very edge
>of the characters are being switched rapidly on and off.  Not sure of the cause
>of this, whether jitter inn the power supply to the screen or jitter in the
>analogue signal from the card; but it would seem to indicate that the screen
>pixels are being constantly 'refreshed' at the scan-rate of the vga card.
>  
>
As I said above, if there is a signal change, the pixel will get changed 
but as long as the signal stays constant for that pixel, it is not changed.

The problem you are stating above could be from your monitor cable 
passing a power cable or some such, next time you are in this mode, try 
moving the cable and see what happens.

Andrew Farnsworth
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