Why does LCD seem to fade when cleared?

M

MearCat

Member
I use a 20x4 character LCD module for some testing but for while I've been curious to why the rate at which it clears the display is so slow. (I am currently using a 08M and a Phanderson #117 serial chip). When I send a clear command to the LCD, the text fades out over a period of around 500-600ms (see code below). I'm curious on why it fades because I have another LCD which when this code is used, the text flashes because the LCD is cleared so quick.

Is this simply the LCD itself, or is it something I can improve with code, or connections/voltage? Is there a specific spec in a datasheet I should reference when purchasing an LCD display to see if this "fade" could occur?

Code: 
for b10 = 1 to 5 
   SEROUT LCD, T2400, ("Fade")
   pause 500
   SEROUT LCD, T2400, ("?f") 'Clear Screen
   pause 600
next

for b10 = 1 to 5 
   SEROUT LCD, T2400, ("?aFade")
   pause 500
   SEROUT LCD, T2400, ("?a    ") 'Goto Line 1, Char 1 & write over "Fade" text
   pause 600
next
 
N

nick12ab

Senior Member
A link to the datasheet, please.

Response time can be affected by the contrast level if it's too high/low.
 
W

westaust55

Moderator
Ass Nick12am indicates, the LCD response time is likely the prime consideration.

Many basic LCD modules use STN type displays which are slower.
Early PC LCD monitors have slow response for turn off akin to persistence with CRT monitors and thus were not good for fast animation.
Most modern PC monitors now have faster response time and thus refresh and animation without blurring is better.
Suspect the types of LCDs most of us use for our character displays are far from the latest technology or high speed/response times.
 
P

phillid

Member
LCDs need AC going to the segments, otherwise they will fade out when turned off, and sometimes segments can even get stuck so they won't turn off!

Maybe your LCD driver is a poor one and isn't supplying AC to the LCD?

Regards
Phillid
 
N

nick12ab

Senior Member
phillid said:
LCDs need AC going to the segments, otherwise they will fade out when turned off, and sometimes segments can even get stuck so they won't turn off!

Maybe your LCD driver is a poor one and isn't supplying AC to the LCD?

Regards
Phillid
Click to expand...
Since LCD drivers seem to be stolen from manufacturer to manufacturer it seems unlikely. A failed driver that isn't driving an LCD properly will usually have the darkness of each column of pixels change depending on the amount of pixels in that column.
 
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