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???
02/26/08 12:04
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 		 #151480 - ports1-3 vs. port0
Responding to: ???'s previous message
Lynn Reed said:
The 8051 ports require a peak current of 660uA to force a zero on an input. You can't do that with a 100K series resistor. You need a resistor below 3K to make it work.


Absolutely.

Brian, please note that there3 is a huge difference between port0 and port1-3 structure.

JW


PS. I have encountered a similar design error in a device I inherited and had to write firmware for. The quick-n-dirty fix was to put a short zero pulse on the pin before reading in its status.


List of 40 messages in thread
TopicAuthorDate
P3.5 input problem            01/01/70 00:00      
   100k is way too large            01/01/70 00:00      
      Yup            01/01/70 00:00      
      ports1-3 vs. port0            01/01/70 00:00      
      a small correction            01/01/70 00:00      
   Page 4 datasheet says            01/01/70 00:00      
      Calculating the maximum resistor            01/01/70 00:00      
         Calculating the ...            01/01/70 00:00      
   80uA is not a maximum specification            01/01/70 00:00      
      re:resistor            01/01/70 00:00      
   Resistor            01/01/70 00:00      
      I would not            01/01/70 00:00      
         Resistor            01/01/70 00:00      
            Resistor ... again ...            01/01/70 00:00      
      basic troubleshooting first            01/01/70 00:00      
         the sensor and its application            01/01/70 00:00      
            Oh, max frequency is ~4kHz :-)            01/01/70 00:00      
         Please ignore the "basic troubleshooting"            01/01/70 00:00      
         pray tell why            01/01/70 00:00      
            Capacitance problems ...            01/01/70 00:00      
   You have totally misunderstood the situation            01/01/70 00:00      
      thank you Kai            01/01/70 00:00      
         maybe it is            01/01/70 00:00      
            Link in original post            01/01/70 00:00      
            datasheet            01/01/70 00:00      
         Being paranoid is a good attitude...            01/01/70 00:00      
            Paranoia medicine            01/01/70 00:00      
               Yes, perfect, i also thought about this...            01/01/70 00:00      
                  the "industrial strength" 485 transciever            01/01/70 00:00      
                     But they gaurantee this            01/01/70 00:00      
      But the micro port shouldn't be driving anything            01/01/70 00:00      
         Missing the boat.            01/01/70 00:00      
            Waving at the boat.....            01/01/70 00:00      
               wrong place (in some instances)            01/01/70 00:00      
            More about the P3.5 pull-up issue            01/01/70 00:00      
               one simple way            01/01/70 00:00      
               AT89S8252            01/01/70 00:00      
         Please read this...            01/01/70 00:00      
   ABS & Safety            01/01/70 00:00      
      safety concerns            01/01/70 00:00      

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