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???
02/09/05 09:17
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 		 #86969 - An experiment - AT89C8252
Responding to: ???'s previous message
The experimental setup was the following: an AT89C8252, P2.0 pulled down using a 20kOhm resistor (to reveal difference between strong and weak internal pullup), scope probes attached to P2.0, the following "program" downloaded and run:
Save This Code
   org  0
   ljmp Start
   org  100h
Start:
   mov  p2,#0FFh
Loop:
   mov  dptr,#0
   movx a,@dptr
   mov  dptr,#0FFFFh
   movx a,@dptr
   nop
   movx a,@r0
   sjmp Loop
The resulting pattern is:



Hence the answers (at least for this particular piece of AT89C8252) to my questions are:
1. No strong pullup of P2 pins during and/or after movx @Ri
2. 2 oscillator cycle strong pullup of P2 pins after movx @dptr (to recover value of P2 SFR on P2 pins)

Answer #1 implies, that it is a good idea to use external pullups on P2 when using it as the high part of address bus, and planning to use movx @Ri.

Jan Waclawek

List of 29 messages in thread
TopicAuthorDate
P2:R0 as memory pointer            01/01/70 00:00      
   Read the cpu data!            01/01/70 00:00      
   P2 readback            01/01/70 00:00      
   Re            01/01/70 00:00      
      Thank you all            01/01/70 00:00      
         Interesting            01/01/70 00:00      
            very well described            01/01/70 00:00      
               This is NOT in the            01/01/70 00:00      
                  ch3 pg 6            01/01/70 00:00      
                     none of them            01/01/70 00:00      
                        more            01/01/70 00:00      
                  An experiment - AT89C8252            01/01/70 00:00      
                     not necessarily            01/01/70 00:00      
                        sure not necessarily            01/01/70 00:00      
                           talking about memory            01/01/70 00:00      
                  MOVX multiplexed with P2 SFR data            01/01/70 00:00      
                     Now I say: HUH            01/01/70 00:00      
                        huh            01/01/70 00:00      
                           Thank you            01/01/70 00:00      
                              what datasheet says            01/01/70 00:00      
                                 I should've RTFM... :-)            01/01/70 00:00      
                              not too much logic            01/01/70 00:00      
                                 sure            01/01/70 00:00      
                     The horses mouth            01/01/70 00:00      
                        horse is plural            01/01/70 00:00      
                           I'd be happy to ...            01/01/70 00:00      
                              can't find them            01/01/70 00:00      
                                 As you use to say :)            01/01/70 00:00      
         another note            01/01/70 00:00      

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