Larry's Blog

PROGRESS WITH LIQUID CRYSTAL DISPLAY

I have developed several subroutines which have been tested and work pretty well.
dspyon - turns display on showing what is in memory
dspyof - turns display off
strtln - specifies line in mem for top of display
shftwd - my routine to shift a byte of data serially to DB0-DB7
write - after page, y-addres, and number of writes have been set
and content of byte to be written have been set, it
writes up to 64 byte-columns (1/2 of screen) across the screen
setpg - allows page to be set from 0 to 7
sety - allows Y address to be set from 0 to 64
reset - resets the LCD
enabx - performs an enable, enabling the action specified by the information on
the bus DB0-DB7 and setting of D/I pin and R/W pin.

Today I have been able to generate a few design patterns on the screen, and have been able to scroll the images upwards. I have a routine to clear memory
but I notice from image on screen that one bit is not being deleted leaving 8 lines
across the screen. I can flash whatever is on the screen on & off at whatever rate I choose. Since I am not reading the status, I have to estinmate a delay that is needed by the HD61202 on the LCD. I shortened this delay for speedier operation and I may shorten it even more.

SUCCESS!!! An LCD IMAGE

After much effort, I have made my HELLO WORLD pgm on a graphic LCD.
ALLELUJAH !!!

AN LCD (LIQUID CRYSTAL DISPLAY)

HERE IT IS!

I have set about programming a graphics type liquid crystal display. It's specs are 128 X 64. The RAM memory on the device is like a bit map of the display.
The one's and zeros in memory make up the picture displayed.

I haven't gotten it to work yet , but the hardware and wiring have been completed.

My first program did not do what I wanted and I may not have the correct command protocol for putting my data into the RAM memories. But I am confident I will find the info I want. Stay tuned!

UPDATE ! JUNE 4, 2005
Great news! I looked up the specs on the HD61202u which is called a
DOT MATRIX LIQUID CRYSTAL DISPLAY COLUMN DRIVER
and found that the controls and data bus go directly to these
chips - there are 2 of them -
also, the "instructions" or what I have been calling commands
are identical to what I have been using in my software.

But then, why is my display not working?
The program looks correct , so now the only lines I haven't checked for continuity are pins 1 thru 6. These are control pins including
enable,r/w, d/i, and rst. Aso I will check the 2 select lines, selecting one or the other of the above mentioned driver chips (HD61202).

The 2 chips actually say SAMSUNG N044A but these must be exact replacements
since the specs given me with the chip explicitly say HD61202.
I felt very good though in finding out that I was using the correct instructions or commands.

Those commands by the way are
- display on/off
- display start line
- set page (x address)
- set Y address
- status read
- write display data
- read display data

Note that for a graphics LCD there are less commands than for an alphanumeric LCD, which I will be programming very shortly ( I just received 2 in the mail).