Constraining an unclocked output? - Constraining an unclocked output? Hi, I am trying to achieve timing closure, but have trouble constraining outputs that is not referenced to an external clock. Do I have to define a false path for each output? Replies: Re: Constraining an unclocked output? If a port (e.g., reset_in) is truly asynchronous and handled by a synchronizer, you cut the path from the port to the first synchronized flip-flop: set_false_path -from [get_ports reset_in] Replies: Re: Constraining an unclocked output? Hi, to declare all IO as asynchronous set_false_path -from [all_inputs] set_false_path -to [all_outputs] Replies: Re: Constraining an unclocked output? Thanks, but it is a bit unclear to me how I would define the false path: set_false_path -from [get_pins A*] -to [get_pins B*] ...when -from and -to is the same signal/net/pin? Replies: Re: Constraining an unclocked output? sstrell is right, do you have further queries? Replies: Re: Constraining an unclocked output? If they're completely asynchronous outputs, yes, you would false path them. You can use wildcards in your target for set_false_path if there are a lot of them.