By: Masud-ul-Hasan
21
External Data Memory
•·  64K byte address space.
•·  Indirectly addressable via R0 and R1 in 256 byte segments.
•·  Entire space in indirectly addressable via the data pointer DPTR.  
8051
PORT 2
ALE
PORT 0
WR
RD
RAM(S) or I/O
CE
        DATA OUTPUTS
   ADDRESS INPUTS
R/W
OE
   ADDRESS LATCH
DECODE