View Full Version : Need Help parallel LCD

Eviatar Tsadok
02-08-2007, 05:20 PM
I've propeller conneted to parallel LCD, I did download example from code exchange.
But I have problem to make it work, I did double check the connection, I tested it with few LCD.

The LCD works with +5V, do I need pull-up resitors? I did try with 10k on DB and E connection.

It seems that the LCD keep present only the black on the first line.

Can someone HELP?


02-08-2007, 06:52 PM
Normally 5V parallel LCD's will accept 3.3Volt logic levels. They will see everything below 0.8 Volt as '0' and everything above 2.0 volt as '1', but check the documentation of the LCD in the chapter that says "electrical characteristics".

Have you remembered to add a potentiometer (or resistor divider) for the contrast regulation?
Usually it's a 10K potmeter with the wiper connected to pin 17, and the other two pins to +5Volt and -5Volt

Also don't forget the reset capacitor connected to pin 16. If you put the capacitor between ground and pin 16, and use a pullup, then the LCD will reset to "Motorola mode".
That means you end up with pin 4 as E (Clock enable) and pin 5 as R/W (read/write). That might not be compatible with the driver software.

Normally you connect the reset capacitor between 5V and pin 16, and use a pull down resistor. Then the LCD will start in "Intel mode".
Pin 4 will become /RD (read pulse), and pin 5 will become /WR (write pulse).

Intel mode is the more common way to drive LCD's so perhaps the propeller driver uses it too.

Otherwise, just check your wiring again.


Eviatar Tsadok
02-08-2007, 08:17 PM
Thanks mahjongg for your quick reply,

I use standard Hitachi 44780 or compatible, with standard 14 pins 2x7 connectors.
I do not know about Intel or motorola mode, it has DB7-DB0, E, RS and R/W bus.

On pin 3 I did put 20K potentiometer and set it right until you can see the gray dots after power up.

In the code, I change the pins definitions to the proper numbers.

After the LCD boot up - nothing happend.

I've checked the voltage on each pins with small program that switch 0-1, the voltage was less 0.2V for 0, and more then 3V for 1

Eviatar http://forums.parallax.com/images/smilies/smhair.gif

02-08-2007, 10:23 PM
The Hitachi 44780 uses a simplified interface connector with only 14 pins, not the normal 20 pins interface that most other parallel mode LCD's use.

The input levels should be OK, you can download the datasheet of a Hitachi 44780 here:

www.datasheetarchive.com/search.php?q=44780&sType=part&ExactDS=Starts (http://www.datasheetarchive.com/search.php?q=44780&sType=part&ExactDS=Starts)

The consequence of using only 14 pins is, among other things, that the LCD module does not have a Reset input, and will always start in motorola interfacing mode.

I am fairly certain thats the problem, because I assume the driver might use the more popular Intel mode.

It should be easy to fix the code though. Maybe you can even turn on an option to switch to Intel mode.
Where can I find the driver code you are using, I can have a look at the code to see if my theory is correct.