and indirect addressing modes are allowed. SFRs may only be directly addressed while upper 128 bytes
of RAM may only be indirectly addressed.
Figure 4.8(a) Directly addressable and (b) indirectly addressable internal RAM area of MCS-51
Higher
128 bytes
of internal
RAM
FFH
80H
7FH
00H
(a)(b)
SFRs
Lower
128 bytes
of internal
RAM
Directly
addressable
locations
of RAM
7FH
00H
Lower
128 bytes
of internal
RAM
Indirectly
addressable
locations
of RAM
FFH
80H
SFRs
FFH
80H
available
only in
XX52 and
above
Higher
128 bytes
of internal
RAM
FFH
80H
available
only in
XX52 and
above
4.4.8 |Reading from I/O Ports
In Chapter 3, it was mentioned that MCS-51 por ...
Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month, and much more.