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???
08/12/04 08:58
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 		 #75799 - RE: Using Port2 for RAM & I/O simultaneously
Responding to: ???'s previous message

Generally, you should avoid it. If your hardware uses external memory access then it is not so hard to implement extra input/output ports as memory mapped ports.


Well i think this is the best part of the message. If you can have a few logic gates just use that and a latch to have a full port, this will be just so much pain avoided in the code that you might even gain.

if this is sram, it is possibly to store user values, (i hope you are using a 8051 derivative with onboard ram & rom) , then you could maybe "bitbang the memory acess, using function


2) using read-modify-write instructions and Ri instead DPTR, something like:
CLR P2.7
SETB P2.5
; ...
ANL P2,#11111000b ; mask address bits
ORL P2,#HIGH(MEM_ADDR) ; prepare high byte of address
MOV R0,#LOW(MEM_ADDR) ; load low byte of address
MOVX A@,R0


i would personally replace the
ORL P2,#high(MEM_ADDR)

by

MOV Ri, #high(MEM_ADDR)
ANL Ri, #00000111
ORL P2, Ri

or any corresponding code (I m no 8051 asm specialist)
to avoid the modification of output bits if a wrong address is provided (maybe is it useless, code should be perfect ;-))


List of 17 messages in thread
TopicAuthorDate
Using Port2 for RAM & I/O simultaneously            01/01/70 00:00      
   RE: Using Port2 for RAM & I/O simultaneously            01/01/70 00:00      
      RE: Using Port2 for RAM & I/O simultaneously            01/01/70 00:00      
   RE: Using Port2 for RAM & I/O simultaneously            01/01/70 00:00      
      RE: Using Port2 for RAM & I/O simultaneously            01/01/70 00:00      
         RE: Using Port2 for RAM & I/O simultaneously            01/01/70 00:00      
            RE: Using Port2 for RAM & I/O simultaneously            01/01/70 00:00      
            RE: Using Port2 for RAM & I/O simultaneo            01/01/70 00:00      
         RE: Using Port2 for RAM & I/O simultaneo            01/01/70 00:00      
            RE: Using Port2 for RAM & I/O simultaneo            01/01/70 00:00      
               RE: Using Port2 for RAM & I/O simultaneo            01/01/70 00:00      
                  RE: Using Port2 for RAM & I/O simultaneo            01/01/70 00:00      
                     RE: Using Port2 for RAM & I/O simultaneo            01/01/70 00:00      
   Only as an input?            01/01/70 00:00      
      RE: Only as an input?            01/01/70 00:00      
         RE: Only as an input?            01/01/70 00:00      
            RE: Only as an input?            01/01/70 00:00      

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