The document discusses external memory for microcontrollers like the 8051. It notes that the original 8051 had 4KB of internal ROM, but more memory could be added externally using suitable circuits. It explains that the EA pin determines whether instructions are fetched from internal or external memory, and connecting it to high or ground selects internal-only or external-only modes respectively. Additionally, it introduces the PSEN pin which is used as a chip select for reading from external memory when in combined or external-only modes.

1. EXTERNAL MEMORY
SEMINAR BY:
DEEP R SHAH
CSE DEPT II YEAR

2. MEMORY ORGANISATION
If the internal memory is
inadequate ,you can add
external memory using
Suitable circuits

3. The original 8051 Micro controller
has 4kb of internal ROM
For this the EA PIN should be
pulled High.when it’s high it
fetches instructions from the
internal memory and if it exceeds
then it fetches from external
memory

4. IN SOME SCENARIO YOU WANT TO IGNORE THE INTERNAL
MEMORY AND FETCH ALL THE INSTRUCTIONS FROM THE
EXTERNAL MEMORY,THEN THE EA PIN SHOULD BE CONNECTED
TO THE GROUND (GND)
FOR THE COMBINATION OF EXTERNAL AND INTERNAL MEMORY –
CONNECT THE EA(EXTERNAL ACCESS)PIN TO +5V.
FOR ONLY EXTERNAL MEMORY –CONNECT EA PIN TO GND

6. PSEN stands
for Program
Store Enable.
It is output,
active-low
pin. This is
used to read
external
memory

12. --THANK YOU--