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???
06/13/05 10:36
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#94760 - No worry...
Responding to: ???'s previous message
Musharraf said:
Upon reset, the pins are initialized as high impedence inputs. However, I have read that floating inputs are not a good thing to have in a system (Especially if it is in strong electric and magnetic fields).

They aren't floating, they are pulled high by a weak internal active pull-up. And if you don't connect anything to these pins, then they aren't susceptible against noise and interference.

The issue with the increase of supply current has to do with the input voltage to internal input gates, which are also connected to the port pins internally: If these get input voltages which are not identical to the supply 'rails', means either 0V or Vcc, then there's an increase in supply current of these individual input gates. This has to do, with the certain topology of CMOS gates, where a PMOS and NMOS transistor are connected between the supply rails, and where a change in input voltage makes the one to partially turn-off and the other to partially turn-on. Especially in applications, where a battery backed-up CMOS RAM is used, even only a slight differ of input voltage from supply rails can make the battery extremely leak! But here we have indeed floating inputs, unless pull-ups or pull-down are connected to each input.

But again, with your application you have already pull-ups which prevent such an increased supply current.

Kai

List of 28 messages in thread
TopicAuthorDate
Minimizing port pin currents            01/01/70 00:00      
   Old threas            01/01/70 00:00      
      Thread Vs Reply            01/01/70 00:00      
         What would be good            01/01/70 00:00      
         for me it does            01/01/70 00:00      
            Re: for me it does            01/01/70 00:00      
   No worry...            01/01/70 00:00      
      but            01/01/70 00:00      
         Sorry, I misinterpreted Musharraf            01/01/70 00:00      
            low power            01/01/70 00:00      
               re            01/01/70 00:00      
                  TI ?            01/01/70 00:00      
                     Total agree            01/01/70 00:00      
                  low power MCUs            01/01/70 00:00      
                     App notes            01/01/70 00:00      
                        Any link for low power appnote?            01/01/70 00:00      
                           Damn all            01/01/70 00:00      
                              static current?            01/01/70 00:00      
                     very low frequencies            01/01/70 00:00      
                        it's not just CMOS            01/01/70 00:00      
                           Biasing generator for the substrate?            01/01/70 00:00      
                              flash?            01/01/70 00:00      
                                 consumption overview            01/01/70 00:00      
                                 SiLabs Wins Then?            01/01/70 00:00      
                                    I don't know            01/01/70 00:00      
      Do worry!            01/01/70 00:00      
   High impedance            01/01/70 00:00      
      Battery powered circuits            01/01/70 00:00      

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