LCD.C library

sjharris · Joined: 11 May 2006 Posts: 78

Hello all,

I have recently purchased a TRI-T 20x4 LCD Display and I am trying to interface a 16f877 to it. I am using the LCD.C library to control the LCD, using the lcd_init() functions etc.
I am unfortunately unable to initialise the screen and display anything on it. I have not controlled an LCD before and do not know where to start checking for errors.
I have connected the PIC pins (D0 - D7) to the LCD lines
D0 - Enable
D1 - RS
D2 - R/W
D4>D7 - D4>D7

The screen is TMBC20443B
datasheet 1 http://3t-lcd.com/TMBC20433B-XX.pdf
datasheet 2 http://www.zxstevefiles.yolasite.com/resources/pdf1.pdf
Any help would be most appreciated

SHarris

Ttelmah · Guest

Have you also connected the power as shown in figure 5.1, on the first sheet. You _need_ the Vcl or Vee connection, before anything will be 'seen'. The GND connection for the display, needs to be the same line as the 0v for the PIC.

Best Wishes

sjharris · Joined: 11 May 2006 Posts: 78

Gnd connection is same as PIC (it comes from same VRegulator)
I have connected as in 5.1
+5 ----[res]------[res]-----GND
....................|
................VCI tap

(Ignore the dots, the bulletin board script ignores whote space!!)

Its about 3V going into VCI.

sjharris · Joined: 11 May 2006 Posts: 78

Looking at the lcd.c source (with CCS install) should this library work with this screen, I dont know what to look for in the source to ensure that it is working?

Thanks

sjharris · Joined: 11 May 2006 Posts: 78

I have now got to the point where I am trying to understand the lcd_init() function. I am trying to re-write it in my code with the timings / settings needed to control the LCD.
Reading the LCD controller http://www.lcdshop.uk.com/dpdf/S6A0073.pdf it seems that if I want to talk to the LCD in 4 bit mode I need to send each string twice.
Is this correct for control bits??

(The only function I am trying to change from lcd.c is the lcd_init)

Here is what I am doing: (TAKEN FROM PG 13 of Datasheet from
http://www.zxstevefiles.yolasite.com/resources/pdf1.pdf)

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

According to your link here, the LCD has a solder-bridge jumper option
on the back. It can be jumpered for SPI mode or the normal 4/8 bit
parallel interface. Look on the back of your LCD to see which way it's
jumpered:
http://3t-lcd.com/TMBC20433B-XX.pdf

Your LCD can probably be used with the Flex lcd 4x20 driver:
http://www.ccsinfo.com/forum/viewtopic.php?t=28268

On page 11 of the following link, in the Extended Function Set section,
it shows there is a bit to enable 4-line mode. That bit needs to be set = 1
for your LCD.
http://www.zxstevefiles.yolasite.com/resources/pdf1.pdf
I think you can do this by modifying the init table in the Flex driver.
Change the number of elements to 5, and add one line, as shown in
bold below:

SteveyG · Joined: 11 May 2009 Posts: 1

3V on Vee is a bit high, you'll probably see nothing on the LCD. The typical range is usually more like 0.8V to 1.6V.

Guest · Posted: Thu Jun 04, 2009 3:46 am

After I have added the extra line

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

If you're using the Flex 4x20 lcd driver from here,
http://www.ccsinfo.com/forum/viewtopic.php?t=28268
then the for loop uses 'sizeof' to find the size of the array.
In other words, it's done for you, automatically.

Guest · Posted: Thu Jun 04, 2009 4:37 am

I have now implemented the Flex driver code but I still cannot add the 5th INIT string (the LCD seems to freeze / not respond to putc etc commands).
Heres what I get:-
Without the Extended Function Control (Four Line Mode)
(I try to display 1, 2, 3 or four depending on what line it is)

Guest · Posted: Thu Jun 04, 2009 9:04 am

I have had a good re-read of the data sheet and it says that to use the Extended Function Set (on page 11) the RE pin has to pulled high, is this done from my uC??
Is the RE pin on the LCD the same as E (PIN 6)??
Thanks
Steve

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

You're correct. There is an enable bit. Add the following changes:

Guest · Posted: Fri Jun 05, 2009 1:17 am

I had the same confusion,
I have spent the last number fo hours trying to find where that bit is set!!

Thanks for your help, I will attempt the changes today.
Steve

Guest · Posted: Fri Jun 05, 2009 1:48 am

Hmm,
I thought that was it!!
Obviously not!!
I have added the extra lines into the LCD_INIT_STRING but the screen now displays
'1' on line 1
'2' on line 3 (in effect line 2)
'}}}}}}}}}}}}}}}' starting at 9 bytes along line 2
'}}}}}}}}}}}}}}}' starting at 9 bytes along line 4

Thanks
Steve

sjharris · Joined: 11 May 2006 Posts: 78

When I return the LCD to two line mode (remove the extra LCD_INIT_STRING) and I try to print something to 17,1 it also copies the data to 1,2 (physical line 2, i.e. second line down). Does my LCD think its a 4 x 16??
Something is not right here, still cant work it out!!
Steve

edit edit edit:
ARGH Sorted it!!!!!

For some reason in four line mode the screen filled half of line 2 and 4 with funny data, when I cleared the screen, again, I was able to write successfully to all four lines.

THANKS ALL FOR YOUR HELP!!!
Steve