Using async signal
Guest
#2405053
Hi, i'm new to VHDL, i have this problem: i've an async signal, called REQUEST, and into my process, if the counter arrives to 5 and if the REQUEST signal went 1 in the previous period of clock, i must do something. my problem is that REQUEST is asynchronous, and its period should be less long than clock's period, so i can't check it every positive edge of clock with the usual clock'event and clock='1'…. how can i solve this problem? thanks! > and if the REQUEST signal went 1 in the previous > period of clock, i must do something. Lets say these are your signals: (X=signal change) CLK .-------. ,-------. ,-------. ,-------. ´ `-------´ `-------´ `-------´ CNT X 3 X 4 X 5 X REQUEST when does it get active? ^here ^or here > and its period should be less long than clock's period, so i can't > check it every positive edge of clock with the usual clock'event > and clock='1'…. You can store a pulse in a signal shorter than your clock cycle in a way like this: http://www.lothar-miller.de/s9y/archives/19-Kurzer-Spike-in-Puls-umgewandelt.html But even a trick like this doesn't help you with your problem of clock donaim crossing. As you describe it, I see no chance to react reliable in less than one clock cycle...
Guest
#2405241
i don't know when request go 1, it's the problem… i think also that the link contains the solution for my problem, thanks!
Guest
#2414961
Hallo, check the signal with a much faster clock and store it with an flip flop. Is that no option? Or use the request signal in the following way "request'event" and set a flag. Sim Reply |