I have a 16×2 LCD shield that I have tested to be working fine when connected to arduino uno using the following pin connections:
3: RW
5: EN
6,7,8,9: DATA(4 bit mode)
The contrast is nice and dark and the text gets displayed properly.
However when I make the same connections to a UNO + Ethernet Shield two things happen
1. The contrast goes all light
2. LCD does not get initialized (row of black boxes)
As per the page here the ethernet shield uses the pin D2, D4, D10-D13, hence i chose the pin assignment above.
Now this has stumped me, why would adding the shield make a difference? Any ideas ??
Best Answer
As suggested by user ben, the issue was that the ethernet shield was using pins that I was trying to use for the LCD.
On page here, the comment by user "njohnson" states that the shield uses all the digital pins except 1,2 and 8.
Moving the LCD pins to the 6 analog pins (as outputs) solved the issue.