Hello,
I’m working on a project that has 8051 and lcd, the lcd driver has no problem. Indeed I used it for a month and it used to work perfectly fine. But last night I was adjusting my voltage supply(which uses 723) and at the same time LCD and 8051 were on and connected to the same voltage supply. I was working on parts of voltage supply that are unrelated to the part that supplies 5V needed to run 8051 & LCD. The most probable thing that I think has happened is a voltage drop on 5V side but I’m not ruling out the possibility of over voltage. Any way what happened was that LCD became weird.
It shows the characters & words exactly as before(so 8051 is well) but some parts of LCD shows very dark lines (quit randomly) and most characters(randomly) show a relatively dark shadow so reading the words are difficult. I tried to reduce contrast as much as possible, it alleviates the problem but still shadow of randomly dispersed dark lines are present.
The LCD is marked LIT204A(4X20) but no manufacturer mentioned! I think it is made in Taiwan. It is not one LCD that worries me because after holidays I will buy new ones. But I don’t know what went wrong so I am worry that it happens in the end product, does anybody encountered same problem ? what can cause this behavior ?
I also want to say that I’m going to use the code that michael karas has sent to this forum for 4X4 keypad, I was going to write a more efficient code in assembly, but when I translated his code to assembly, I saw I hardly can write a better code( it was beautiful)!!! I want to thank him, I learned many things from him and other members and I owe him much. I hope some day I can help other people the way he helps people!

Thank you very much