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Problem with the pin of the character LCD on Cyclone III FPGA Development Kit

Honored Contributor II



I have a problem, i try to use the PIN of the character LCD for other input/output.  

And i have a problem, the output is at 0.9V for a low signal, and at 1.9 for high signal. I set the voltage to 2.5(default)(2.5V doesn't change) on the pin planner. 


I don't really unsderstand, why is not 2.5V or 0V. I have a signal that i always put at 0, and the ouput voltage of this one stay at 0. 



I have to use those PIN and not others ones. 

Thank you.
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2 Replies
Honored Contributor II

What is the pin, and device you are using and the exact FPGA development board you are using? 


It sounds like you are trying to drive a higher current load than the output can handle.. 


Typically you will not get 2.5 and 0, because there is still the transistor drop to consider, but the 2.5 CMOS output should still be able to proved 2.0 and 0.4 at it's state current drive strength. 


If you are attempting to drive a higher load current then the rated level, then 1.9 and 0.9 levels are possible. 


Honored Contributor II

Where are you testing the voltage? Is this really the voltage on the fpga pin? 

Maybe you are testing on LCD pin and you have a series resistor between. 

(this is just an idea, I don't know your board layout)