# SparkFun LCD what to put into Vee

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#### excetara2

##### New Member
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.

http://www.electro-tech-online.com/custompdfs/2009/03/GDM12864H.pdf

#### crutschow

##### Well-Known Member
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.

#### blueroomelectronics

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

#### excetara2

##### New Member
Almost

**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!

Last edited:

#### duffy

##### Well-Known Member
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.

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