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???
12/26/04 07:59
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 		 #83876 - Code segment adr space VS Xmem adr space
Responding to: ???'s previous message
I wonder your HW design, your 64KBytes Flash EPROM should be in Code segment adr space that activated by PSEN. While your 8255 should be located in XMEM adr space and activated by RD & WR. So there should be no address space contention!?! If such arrangment, there is no need for special decoding arrangment, just connect the 8255 to A0, A1 and activate the 8255 by RD & WR and you will get a memory map of a 64Kbytes ROM code address space and a repeating of 8255 (4 ports) in the XData that can be referenced by DPTR, or @Rn ..etc. If you want to save more XDATA addr space, just use some gates to arrange your pattern to select the 8255 (enable CS instead of hardwired always selected CS)...etc.
Think and you will find there are lots of simple ways....
Happy 8052'ing and best 73 from Li.


List of 31 messages in thread
TopicAuthorDate
Hardware problem            01/01/70 00:00      
   Address decoding            01/01/70 00:00      
   Use OR            01/01/70 00:00      
      Jan Waclawek            01/01/70 00:00      
   Adress decoding            01/01/70 00:00      
   instead of the 8255            01/01/70 00:00      
   Code segment adr space VS Xmem adr space            01/01/70 00:00      
   Why the 8255 ?            01/01/70 00:00      
      Steve M. Taylor            01/01/70 00:00      
         Farnell Distributor in Iran            01/01/70 00:00      
            Disturbutors donot supply many chips            01/01/70 00:00      
               Re: Disturbutors donot supply many chips            01/01/70 00:00      
                  Quite off-topic now            01/01/70 00:00      
         alternatives?            01/01/70 00:00      
   Check for a sinple gate            01/01/70 00:00      
   8254+1            01/01/70 00:00      
      Who ever said the 8255 was for x86?            01/01/70 00:00      
      a rebuttal            01/01/70 00:00      
         rebutal            01/01/70 00:00      
            psd            01/01/70 00:00      
            decoder            01/01/70 00:00      
         Item #2 Rebuttal            01/01/70 00:00      
            not me            01/01/70 00:00      
      Atmel Disturbutor in Iran            01/01/70 00:00      
         Thanx Farshid.            01/01/70 00:00      
            chips            01/01/70 00:00      
               Dear Steve            01/01/70 00:00      
                  How many ?            01/01/70 00:00      
                     AT89C51SND            01/01/70 00:00      
                        SMD soldering iron?            01/01/70 00:00      
                     there is no market in Iran for them            01/01/70 00:00      

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