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???
06/10/08 00:22
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 		 #155648 - I hav no desire to look up 40xx chips, but ..
Responding to: ???'s previous message
Unless he uses a very slow process (possible, but not verified so far), and repeats the sampling sequence multiple times he can easily capture a "wrong" state during the bounce (typically 20 ms).
... his shift register MUST be latch and shift
if there is no latch the chip is wrong, if there is, the stuff Richard posts is wrong.

if the SR is latched each "bounce time" there is no difference (in the respect of bounce) between reading from a Shift register and direct pin input.

Erik


List of 42 messages in thread
TopicAuthorDate
Input Protection            01/01/70 00:00      
   I use a series resistor            01/01/70 00:00      
      I like clamps ...            01/01/70 00:00      
         I would not use a \'S\' chip            01/01/70 00:00      
            It's just an array of schottky diodes, Erik            01/01/70 00:00      
               Resistors and cap            01/01/70 00:00      
                  why the slowpoke            01/01/70 00:00      
                     the technology will still work in this case            01/01/70 00:00      
                        stupid boss            01/01/70 00:00      
                           ... or stupid Erik, maybe?            01/01/70 00:00      
                              I did NOT say "stupid engineer"            01/01/70 00:00      
                                 now, don't get me wrong here ...            01/01/70 00:00      
                                    a typical result of a stupid boss            01/01/70 00:00      
               well the 74S had me since ....            01/01/70 00:00      
                  Yes, it indicates the process technology            01/01/70 00:00      
                     HEF4021            01/01/70 00:00      
                        Anyhow the major setback using 40xx            01/01/70 00:00      
                           This is entirely wrong!            01/01/70 00:00      
                        No, not better, but different            01/01/70 00:00      
      Adding another cap            01/01/70 00:00      
         I do not think so, but it will wear the switch            01/01/70 00:00      
         Immunity against what?            01/01/70 00:00      
   No, just a business decision ...            01/01/70 00:00      
      Uhm...            01/01/70 00:00      
         all 40xx chips are based on the same technology ..            01/01/70 00:00      
         if the RC before the PISO doesn't do it ...            01/01/70 00:00      
            Values            01/01/70 00:00      
               I do not know why ...            01/01/70 00:00      
                  Values..            01/01/70 00:00      
                     like this            01/01/70 00:00      
                     Caps and RF immunity            01/01/70 00:00      
                        true - and not            01/01/70 00:00      
                           Expensive capacitors?            01/01/70 00:00      
            BALDERDASH            01/01/70 00:00      
               the PISO register is loaded only once ...            01/01/70 00:00      
                  I hav no desire to look up 40xx chips, but ..            01/01/70 00:00      
                     If there's nothing pressing ...            01/01/70 00:00      
                        Setup            01/01/70 00:00      
                           overdoing it            01/01/70 00:00      
                           That just might be adeuqate ...            01/01/70 00:00      
                              Switches            01/01/70 00:00      
                                 IF you choose the right rate ... and IF you check            01/01/70 00:00      

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