Can anyone tell me how to connect DE kit to TTL signal.I need to connect the kit to rotary encoder,the voltage input of 2 slots(40 pins) in DE kit is 0-3.3V,the pulse which the encoder create is 0-5V.I used a pull-up resistor like the image,but when connecting,the kit didn't realize the trigger-edge of the pulse (if rising_edge(GPIO_0(0)) then...) Thanks for your help. http://i452.photobucket.com/albums/qq242/toporice/untitled.jpg http://www.alteraforum.com/forum/%5BIMG%5Dhttp://i452.photobucket.com/albums/qq242/toporice/untitled... http://www.alteraforum.com/forum/%5Dhttp://i452.photobucket.com/albums/qq242/toporice/untitled.jpg
DE-1 has no clamp diodes at GPIO pins, so the input voltage should be basically limited externally. A resistive divider can do as a simple solution, otherwise 3.3V logic devices with 5 V input capability, e.g. 74LVC or VHC family, can be used as level translator.