Please Help me On LCD Concept

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Thota Suresh Avionics

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hi,

im using 16x2 lines hd44780 lcd ,



according to data sheet rs=0,r/w=1 high means read mode,this mode is used while reading busy flag,



rs=1,r/w=1 means reading contents of the CGRAM,DDRAM...



lcd is output device, what is the use of reading DDRAM/CGRAM contents? is there any real time application regarding this mode of operation??

if yes please let me clarify what are they???
 

CGRAM is RAM for storing the bit patterns for the eight user-defined characters, non-standard character types that are not in the CGROM. You can load your own dot pattern shapes into CGRAM and using certain reserved codes in DDRAM, call these up for display.

DDRAM - stands for "Data Display Random Access Memory" and is the working data buffer of the display. Each character on the display has a corresponding DDRAM location and the byte loaded in DDRAM controls which character is displayed.


https://www.8051projects.net/lcd-interfacing/basics.php




Best regards,
Peter
 



Hi Peter and katela ,
Thanks for your replies.

I guess you hadn't got my question,

In Manual it is mentioned,

rs = 0, rw = 0 -- send command to LCD
rs = 1, rw = 0 -- send data to LCD .

rs = 0, rw = 1 -- reads busy flag
rs = 1, rw = 1 -- reads contents of the CGRAM,DDRAM

Normally I worked on programs, where I was sending commands and data for display. I have stored values in CGRAM for making my special chars and called the its address to be displayed on LCD.

But in the conditions "rs = 0, rw = 1 and rs = 1, rw = 1" is there any application where in as we will read what is there in LCD, as LCD is known as output device.
I want to know where that applies ??

regards,
Suresh.
 

Characters set inside LCD is defined by manufacturer. The ROM is part of the main LCD controller (HD44780, KS0066, ...), is mask programmed, and cannot be changed by the user. The manufacturers do offer alternative symbols sets in ROM for European and Asian languages, but most U.S. distributors stock only the standard character set shown in the LCD Serial Backpack manual.

Custom character or graphics can be easily made in MikroE compilers, there is implemented tool for this purpose which generate code for you.


Best regards,
Peter
 

Hi,

Have always wondered the same, why would you need to read the lcd when you wrote it there in the first place ?

Perhaps in some routines it is easier to find out where the cursor / data is on the lcd than from the subroutine that wrote it ??

Possibly in the early micro days when resources were low, you could also use the cgram as a general ram scratch pad to your main program.

Have never see any example of any program reading from the lcd.

This tutorial has reference to reading the lcd on page 195 of pdf2
http://www.epemag.wimborne.co.uk/resources.htm
 

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