----- Original Message ----- From: "Bala Chandar" To: Sent: Wednesday, December 12, 2001 11:01 PM Subject: Re: [EE]: Which is the ideal IC? > I like the suggestion by Tim McDonough of using 4021 that will give 8 > inputs. (74HC165 can also be used, I think, as it looks a functional > equivalent of 4021.) Since I already have two pins working as common Clock > and Data outputs, I can use them for 4021 as Clock and Load outputs. This > means, by using only one pin to receive the serial data, I can get 8 > additional inputs. You can save the additional pin by putting the 4021/74HC165 and your output shift registers all in the same, serial chain. This can also add a bit of a safety feature: if the data to be output is shifted around the ring and back into the processor you can check in software to make sure it didn't get mangled by noise, transients, etc. BEFORE you strobe it to the output latches. A few years back I used this technique in an 8052 based system that had 64 inputs and 32 outputs. The data can be read/written in very little time. Tim -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads