problem in reseting graphical LCD

[hm_fa_da]

hossein vismeh

hi ;

i don't know how to reset a graphical LCD ( GDM12864a)
in it's datasheet is said that the system can be initilialized by setting RSTB terminal at low level when turning power on .

does it mean that i can't reset LCD when it's power is connected and middle of using it ?

if so , i have a problem that my MCU is also being connected to power as while as LCD is being connected , so i can't clr RSTB before power be connected !!!

and what is resetbit in LCD status reading ?

is RSTB active low or active high ?
should i keep RSTB pin low or high until resetbit in status goes low ?

i have tested many ways and got result , but not a good and sure result , for example i connected RSTBpin to vcc and then connected power to both LCD and MCU , sometimes it worked !!! but not all times ....

now i want to know the exact and true way of reseting LCD ?

thanks to all ....

 

[Regnum]

can i connected l c d to p3

which controller does it use?

 

[gidimiz]

gdm12864e example

Hi,

After reading the data sheet for the LCD i can try to answer your questions:
1.

does it mean that i can't reset LCD when it's power is connected and middle of using it ?

No you cant. The rest can happen only when you power the LCD. Like your PC, you cant generat a complete reset while the computer is runing.
2.

if so , i have a problem that my MCU is also being connected to power as while as LCD is being connected , so i can't clr RSTB before power be connected !!!

There are 2 options to solve that:
A. Use a P-Channel mosfet to turn on and off the LCD.
B. Use a capacitor connected between the RSTB line and GND. This will hold the line long enough for the LCD to get a good reset.
3.

and what is resetbit in LCD status reading

If i understand your question, then you have to keep reading using the instruction of Status Read Until BIT DB4 = 0 and BIT DB7 = 0. Only then you can start writing to the LCD.
4.

is RSTB active low or active high

To reset it is active low. Then you will read 1 saying its in reset mode. When you will read it as 0 it will be in Normal mode. See page 19 for the Display Control Instruction
5.

should i keep RSTB pin low or high until resetbit in status goes low

As they say in the Reset section, you have to keep it low for at list 1us After power to the LCD reached 4.5V
6. You need to reset the LCD only once, and thats at power up. After that you can use the LCD with out any problems. Be sure that the reset pin ( PIN 17 in the LCD )will be low for at list 1us using any small capacitor.
Good luck.

 

[hm_fa_da]

ks0107b init

it's driver ic is KS0107b and KS0108b ,

I HAVE TESTED THAT WAYS , I CONNECTED A 10uF CAPACITOR BETWEEN RSTBpin AND GROUND , A 10 Kohm RESISTOR BETWEEN RSTBpin AND VCC , THEN I WROTE THIS PROGRAMM TO CHECK THE STATUS OF LCD , BUT LED DOESN'T TURN ON !!!


CS1 EQU P3.0
CS2 EQU P3.1
EN EQU P3.3
RW EQU P3.4
RS EQU P3.5

JMP 040H
ORG 040H
MOV P1,#0FFH
MOV P3,#11110111B
MOV P2,#0FFH
CHECK: CLR EN
CLR RS
SETB RW
SETB EN
NOP
NOP
NOP
CLR EN
NOP
NOP
NOP
MOV A,P1
JB ACC.7,CHECK
JB ACC.4,CHECK
CLR P2.0
AJMP $
END.

Added after 2 hours 43 minutes:

after a lot of search , i found this file :

www.8052.com/codelib/glcd2.rar

in that project , he didn't use read status or any read function from LCD !!!
and he connected reset pin to VCC without any CAP or resitor ...

it helped me a lot ,
thanks to you all and to that project maker , Hossein vismeh from IRAN .

Added after 2 hours 2 minutes:

at last i found my own program problem , it was just because of using 3 nop between SETB EN and CLR EN and MOV A,P1 !!!!!

i teted it many times and in all result was :
problem is because of using 3 nop between ....

but i don't understand why ???