I just bought the SparkFun LCD:

Graphic LCD 128x64 STN LED Backlight
sku: LCD-00710

I am not sure what to put into Vee from the datasheet. I believe I'm supposed to put in negative voltage like the last LCD I had. I believe it was like -15V but want to make sure. I don't want to fry it.

Link to datasheet:
http://www.sparkfun.com/datasheets/LCD/GDM12864H.pdf

 

According to the "Electical Absolute Maximum Ratings" table Vee can be between Vdd-19 to Vdd+0.3.

So if you are applying +5V to Vdd, then Vee maximum values are between +5.3V to -14V. According to the "DC Electrical Charcteristics" table typical Vee would be -3V to -12V for Vdd=5V.

__________________
Carl
Curmudgeon Elektroniker

 

Many VLCDs have their own -VEE generator, check the datasheet. (You use a 22K pot between +5, VEE & VEE Gen)

__________________
Bill
Smart Kits build Smart People
http://www.blueroomelectronics.com/

 

**Sorry, meant to make this a new topic, this has nothing to do with the Vee**

OK, I've narrowed down the problem. Using a logic analyzer, I realized that my ENABLE signal is not being pulsed (I believe it has to go from 1 to 0 for the instruction to be executed). In the code that I downloaded, it has these two lines:

#define LCD_E_HIGH (PORTD |= (1<<5))
#define LCD_E_LOW (PORTD &= ~(1<<5))

Then, to set ENABLE high or low they simple just use

LCD_E_HIGH; or
LCD_E_LOW;

Does anyone see a problem with these? For some reason they are not triggering the enable. Or can someone explain what the first two instructions do?

Thanks again!

 

The first one says to OR portD with 1 shifted to 10000, the second says to AND it with the complement of 1 shifted to 10000.

This looks way too complicated for a #define compiler instruction. Assign LCD_E_HIGH and LCD_E_LOW to macros that do direct bit manipulation or bit masks.