Got the following infor from the “STEP-MXO2 V2 software manual”:
When the single of LED on the STEP-FPGA is low, the led will be brighten, and initial state of button is high, when you push it, the single of button is low.
So, when the FPGA is running, the led will be brighten if you push any button.
This means:
1. LED is active LOW. When FPGA gives an output LOW, so the connected LED is on! And when the FPGA delivers an logic HIGH output, the connected LED is off.
2. For the push buttons, they give HIGH output when NOT being pressed down. And when a button is pressed, it provides a LOW output