DE10-Lite has no debounced circuit
From Terasic Wiki
Q: There is debounced circuit in the DE10-Lite schematic pdf file, however, there is no debounced circuit (U14 component: SN74AUC17) on the DE10-Lite board, why did this happen?
A: Maybe cutomer's DE10-Lite board is an earlier version, but he/she referred to the schematic file of the new DE10-Lite version. In fact, there is no debounced circuit in the earlier DE10-Lite version.
1. As there is Schmitt Trigger function in the DE10-Lite MAX10 FPGA, which can be used to eliminate bounce, we think there is no need to use an external circuit in the DE10-Lite board or debounce code in the project.
However, according to the feedback from Altera University Program, it seems that the Schmitt trigger function of MAX10 FPGA is not able to eliminate bounce completely. Then we also checked the specification of the MAX10 FPGA and did some experiment, found that the Schmitt trigger range of the MAX10 was small, so it couldn't eliminate bounce in some special conditions.
So, we added the debounce circuit (U14) in our later DE10-Lite version.
2. If customers design their own project with KEY, please make sure the pin IO standard of the KEY is set to Schmitt trigger as the picture below, which will filter the bounce in therory.
If customers still find there is bounce in operation, they can have a try to add debounce code in their project. We recommend customers to refer to DE0 debounce project and then write the code for DE10-Lite board.
The DE0 debounce project is available in this link: http://www.terasic.com.tw/cgi-bin/page/archive.pl?Language=English&CategoryNo=56&No=364&PartNo=4.
