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03/26/06 01:40
Modified:
  03/26/06 01:42
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 		 #113111 - Reason of buffering
Responding to: ???'s previous message
Zeeshan said:
I suppose a 74HC244 will be adequate to buffer /RD, /WR, A0 and A1 lines?

The idea behind the buffering of /RD and /WR lines is, that these lines are most of the time pulled high by only the weak internal pull-up. So, source impedance (about 10...50kOhm) is much higher than the typical 50Ohm of a 74HCMOS output. This results in an increased susceptibility of /RD and /WR lines against charge injection via stray capacitance, means signal integrity on these lines can easily be eroded.
Have a look at /RD and /WR pins of the RAM chips to find out, whether these signals are proper or not.

Kai

List of 78 messages in thread
TopicAuthorDate
Help me - 8052 SBC project !            01/01/70 00:00      
   Why?            01/01/70 00:00      
   Why Not?            01/01/70 00:00      
      wheel-reinvention gone mad!            01/01/70 00:00      
      RoHS?            01/01/70 00:00      
         An EU concern            01/01/70 00:00      
         the other side of ROHS            01/01/70 00:00      
      Reasons - 101 !            01/01/70 00:00      
         Can you buy from India?            01/01/70 00:00      
         leave the guy alone            01/01/70 00:00      
         another illusion            01/01/70 00:00      
            RE: another illusion            01/01/70 00:00      
   Wire-wrap??????            01/01/70 00:00      
      Not quite so ...            01/01/70 00:00      
         A very bad signal to beginners!            01/01/70 00:00      
            Nope ... that's the wrong signal            01/01/70 00:00      
               And what about EMC?            01/01/70 00:00      
                  Just exactly who cares about it?            01/01/70 00:00      
                     RE: Just exactly who cares about it?            01/01/70 00:00      
                        Where do you buy them?            01/01/70 00:00      
                        Consumer Vs Comercial            01/01/70 00:00      
                           emphasizing a point            01/01/70 00:00      
                     Yes            01/01/70 00:00      
   2 RAMs?            01/01/70 00:00      
      I see another "illusion"            01/01/70 00:00      
         RE: I see another "illusion"            01/01/70 00:00      
            There's another approach            01/01/70 00:00      
   Schematics !            01/01/70 00:00      
      /EA not connected !            01/01/70 00:00      
         To ground!            01/01/70 00:00      
            U1 = AT89C52            01/01/70 00:00      
               Ok            01/01/70 00:00      
         RE: /EA not connected !            01/01/70 00:00      
   i see no comment on this            01/01/70 00:00      
      RE: i see no comment on this            01/01/70 00:00      
         Very unsafe, it does not give a "long wr            01/01/70 00:00      
            7.37mhz??            01/01/70 00:00      
               RE: 7.37mhz??            01/01/70 00:00      
                  But why are you reporting...            01/01/70 00:00      
                     RE: But why are you reporting...            01/01/70 00:00      
                        simple things            01/01/70 00:00      
                           Wouldn't it be more helpful            01/01/70 00:00      
                              the reason mainly is "students"            01/01/70 00:00      
                                 I agree completely but here's the thing            01/01/70 00:00      
                                    that is not the issue            01/01/70 00:00      
                                       There's teaching and there's preaching            01/01/70 00:00      
                                          that's the crux            01/01/70 00:00      
                                             Complaining won't help.            01/01/70 00:00      
                                                where is the difference?            01/01/70 00:00      
                                                   Not much of the time            01/01/70 00:00      
                                                      OK, I realized that just after I posted            01/01/70 00:00      
                                                         We have to think of the children            01/01/70 00:00      
                                                            a response            01/01/70 00:00      
                                                               I don't recommend that sort of thing            01/01/70 00:00      
                                          RE: There's teaching & there's preaching            01/01/70 00:00      
                                 RE: the reason mainly is "students"            01/01/70 00:00      
                                    that lazy people exist does not mean you            01/01/70 00:00      
                                       RE: that lazy people exist does not mean            01/01/70 00:00      
                                          OOPS            01/01/70 00:00      
                                             RE: OOPS            01/01/70 00:00      
                                                risky            01/01/70 00:00      
         Bus contention!!            01/01/70 00:00      
            RE: Bus contention!!            01/01/70 00:00      
               Answers            01/01/70 00:00      
               Run the numbers.            01/01/70 00:00      
                  RE: Run the numbers.            01/01/70 00:00      
                     Please try a lower clock frequency!            01/01/70 00:00      
                     Vcc_2            01/01/70 00:00      
                        RE: Vcc_2            01/01/70 00:00      
                     it's not the number of IC's            01/01/70 00:00      
                     D1 = 1N4100 ?            01/01/70 00:00      
                        Would that be a 1N4001?            01/01/70 00:00      
               Reason of buffering            01/01/70 00:00      
                  RE: Reason of buffering            01/01/70 00:00      
                     use a scope            01/01/70 00:00      
      Why would that be?            01/01/70 00:00      
   You might want to use a register            01/01/70 00:00      
   8255: RIP            01/01/70 00:00      

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