In a resistive touchscreen I am trying to read x-y position. The schematics is as followed. The code works fine and when I press a point, it reads correct position well but the problem is in standby ( when no touch ). The ADC shows the middle of the screen both for x and y instead of reading zero ( around 512 in a 10 bit ADC reading ). I set a parallel 4.7 k resistor from X1 and Y1 to ground and the result is better ( it reads around 20 in standby) but I have not seen such design anywhere and dont know which value of the resistor is the best if this is the solution. There is a good tutorial on resistive touchscreens by ATMEL here. In page 4, there is a table about the settings. I couldn't understand what Hi-Z stands for and I think the main result of my problem goes to that pull-up/int in the table for standby , but I couldn't find any sample code for setting a pull-up/int . What is that? should I clear SFIOR register PUD before reading and turning it off during the scan?
Schematics without resistor:
Schematics with resistor: