Email: Password: Remember Me | Create Account (Free)

Back to Subject List

Old thread has been locked -- no new posts accepted in this thread
???
01/27/06 06:43
Read: times


 		 #108462 - yes and no
Responding to: ???'s previous message
hi,

Kai Klaas said:
By the way, the "Bible" itself supports the idea of "input mode" and "output mode", when they write:

"Each I/O line can be independently used as an input or an output. ... To be used as an input, the port bit latch must contain a 1, which turns off the output driver FET."

Phrase "To be used as input" does not mean "set to input mode". Even you write a '1' to latch nevertheless I/O line is still used as output one as well.

Erik pointer right (but emotionaly, yes) that classic 8051 has no port "modes" and some novice people are confused due this term. Just look at original post:

Mohit Gupta said:
I have to initialise the port P1 of the 89C51 as output port with all port lines initialised to a high state i.e. 1.

Now for initialising the port P1 as output, I have to give the instruction
P1 = 0x00

To make all the lines of this port as High, can I give the instruction:
P1 = 0xff;

Will it not make the port P1 as input port?

And so what? Using terms "input and output modes" we should answer: "yes, writing '1's to the port P1 makes it as input port".
Then he asks: "whatta hell, I need to have it as output with '1's!!!". And only after this we start to explain that "in fact, 8051 has no separate input or output port modes, etc...".
So Erik just pointed on this fact. And he might not say better:

Erik Malund said:
mov a,Px will read the voltage on a port pin which, if the port latch is set high can be pulled low by external forces due to the port being quasi-bidirectional. If the pin is set low, the "strength" of the force (see the architecture) holding it low is so that, if an external force try to pull it high, destruction will result


Kai Klaas said:
So, what's so wrong to distinguish between "input mode" and "output mode"? If this is misleading, then the phrase "quasi-bidirectional" also is. It all depends on what you actually mean by these phrases.

I agree; nevertheless Erik doesn`t only name port "quasi-bidirectional" - he also explained what it means.

Kai Klaas said:
By the way, you should think about your relationship to the other forum members. I would never ask you to stop "babbling"!

Well, I think this is just emotions due this question appears often and often.

Regards,
Oleg

List of 51 messages in thread
TopicAuthorDate
initializing a port as output            01/01/70 00:00      
   STOP THE BABBLE            01/01/70 00:00      
      Keil says....            01/01/70 00:00      
         Keil is wrong!            01/01/70 00:00      
            what about the bible itself            01/01/70 00:00      
               the issue is not if someone can find ref            01/01/70 00:00      
                  Dont see any confusion            01/01/70 00:00      
                     what works            01/01/70 00:00      
                     The confusion arises...            01/01/70 00:00      
                        yes that may be the thing            01/01/70 00:00      
                  We talk about the "Bible"!            01/01/70 00:00      
                     it really is a wired or configuration            01/01/70 00:00      
                        No disagree            01/01/70 00:00      
                        I agree, but all are not equal            01/01/70 00:00      
         Confguring......            01/01/70 00:00      
   Quasi bidirectional            01/01/70 00:00      
      NO, NO, NO STOP THE BABBLE            01/01/70 00:00      
         there is only output mode            01/01/70 00:00      
            no, there is NO mode!!!!!!!!!!!!!            01/01/70 00:00      
         Who is babbling?            01/01/70 00:00      
            Maybe Rude but right            01/01/70 00:00      
               Mode clarified            01/01/70 00:00      
                  No, that's wrong            01/01/70 00:00      
                     i see            01/01/70 00:00      
                     Why is this wrong??            01/01/70 00:00      
                        playing with words            01/01/70 00:00      
                           Yes            01/01/70 00:00      
                           "Mode" is the word            01/01/70 00:00      
                              what i meant            01/01/70 00:00      
                  No            01/01/70 00:00      
                     which mode            01/01/70 00:00      
                     lets play with words            01/01/70 00:00      
                  Exception            01/01/70 00:00      
                     see this            01/01/70 00:00      
                     a valid, sometimes overlooked point            01/01/70 00:00      
                        Indeed            01/01/70 00:00      
               Yes, but weak or strong            01/01/70 00:00      
            yes and no            01/01/70 00:00      
               Yes, that's it!            01/01/70 00:00      
                  one more word            01/01/70 00:00      
         What a Rudeness            01/01/70 00:00      
   No input output            01/01/70 00:00      
      Just read the port!!!!!!!!!!!!!!!1            01/01/70 00:00      
         yes            01/01/70 00:00      
            not offending            01/01/70 00:00      
               not really            01/01/70 00:00      
                  see what keil says            01/01/70 00:00      
                     about "rudeness"            01/01/70 00:00      
                        No excuse            01/01/70 00:00      
                           what agression, what rudeness            01/01/70 00:00      
                              Haha!            01/01/70 00:00      

Back to Subject List